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Full text of "Noise barrier design handbook"

• 



I TE 

662 

.A3 

no . 

KHWA- 

RD- 

76-58 



• 



FHWA-RD-76-58 

NOISE BARRIER DESIGN HAMD130 



Transportation 



IGHWAY 







• 



Prepared for: 

U.S. DEPARTMENT OF TRANSPORTATION 

FEDERAL HIGHWAY ADMINISTRATION 



« 



NOTICE 

This document is disseminated under the sponsorship 
of the Department of Transportation in the interest 
of information exchange. The United States Govern- 
ment assumes no liability for its contents or use 
thereof. 

The United States Government does not endorse pro- 
ducts or manufacturers. Trade or manufacturers' 
names appear herein solely because they are considered 
essential to the object of this report. 



• 




Technical Report Documentation Poge 



I. Report No. 



FHWA-RD-76-58 



2. Government Accession No. 



3. Recipient's Cotolog No. 



4. Title and Subtitle 



S. Report Dote 

February 1976 



NOISE BARRIER DESIGN HANDBOOK 



6. Performing Of goni xo lion Code 



7. Author's) 

Myles A. Simpson 



8. Performing Orgonizotion Report No. 

3199 



9. Performing Organi lotion Nome and Address 

Bolt Beranek and Newman Inc. 
1701 North Fort Myer Drive 
Arlington, Virginia 22209 



10. Work Unit No. (TRAIS) 



11. Controct or Grant No. 

DOT-FH-11-8287 



13. Type of Report and Period Covered 



12. Sponsoring Agency Nome and Address 

Department of Transportation 
Federal Highway Administration 
Office of Research 
Washington, D.C. 20590 



Final Report 



• 4. Sponsoring Agency Code 



15. Supplementary Notes 



16. Abstract 



This handbook is intended to be a tool for use by the highway designer to 
aid in the design of noise abatement barriers. It provides a means of de- 
fining the geometric configuration of a barrier to produce a desired noise 
reduction, and also provides a design evaluation and selection procedure in 
which specific barriers are detailed, and then evaluated in terms of cost, 
acoustical characteristics, and non-acoustical characteristics (such as 
durability, ease of maintenance, safety, aesthetics and community accept- 
ance). This handbook guides the designer in the preparation of a design 
which he believes will be accepted by the community and perform as desired 
both acoustically and non-acoustically, for reasonable cost. 



Dept. of Transportation 



MAY 2 1977 



Library 



17. Key Words 



Highway noise, noise barriers, noise 
attenuation, highway construction 
and design 



18. Distribution Statement 



No Restrictions. This document is 
available to the public through the 
National Technical Information 
Service, Springfield, Virginia 22161 



19. Security Classif. (of this report) 

Unclassified 



20. Security Clossif. (of this poge) 

Unclassified 



2). No. of Pages 

265 



22. Price 



Form DOT F 1700.7 (8-72) 



Reproduction of completed poge authorized 



ADDENDUM 

The barrier design curve presented in this manual has been approved 
for use on Federal-aid highway projects. Except at large Fresnel 
numbers, there are no practical differences between this curve and 
the other approved design curves (the NCHRP 117/144, and the Trans- 
portation Systems Center Noise Prediction Model) as illustrated in 
the figure below. The differences among the curves at large Fresnel 
numbers reflect the application of attenuation limits based on field 
experiences of the particular curve's author. 



DO 

T3 

C 
O 

3 
C 
0) 

< 



- 

DO 




.1 1 

Fresnel Number, N 



MAX 



Figure 1. Comparison of approved barrier attenuation curves 
for incoherent line source. 



li 



PREFACE 

This Handbook is the result of research and development con- 
ducted for the Federal Highway Administration under Contract 
No. DOT-FH-11-8287 by Bolt Beranek and Newman Inc., with the 
firm of Wilsey and Ham as subcontractor. Myles A. Simpson 
has been the Principal Investigator. 

Within BBN, the following individuals made major contributions. 
David A. Towers was primarily responsible for obtaining and 
analyzing information on existing barrier constructions through- 
out the country, as compiled in Reference 1-1. The field eval- 
uation study of barrier attenuation reported in Reference 1-2 
was conducted by Myles A. Simpson, with assistance from David 
A. Towers and Harry Siedman. Daniel E. Commins performed the 
literature review also contained in that reference. The scale 
model and analytical study of multiple reflections in walled 
highways and tunnels, described in Reference 1-3, was conducted 
by Dinesh R. Pejaver and John R. Shadley. Parker W. Hirtle, 
Neville A. Powers, and Carl J. Rosenberg investigated the sound 
absorption properties of various materials catalogued in 
Reference 1-4. 

Wilsey and Ham had primary responsibility for consideration 
of cost and non-acoustical characteristics of barriers, and 
for development of the reference drawings contained in this 
Handbook. Kenneth L. Wuest and Steven Vartan were principal 
participants from Wilsey and Ham. 



in 



During the course of this project, Dr. Eugene Chen, Dr. Howard 
Jongedyk and Dr. Timothy Barry have been Contract Managers. 
The author would like to thank them for their support and 
guidance throughout the project. Appreciation is also due 
to personnel from the Offices of Engineering, Environmental 
Policy and Implementation for their useful comments and sugges- 
tions. 

Finally, the author would like to express his sincere gratitude 
to Grant S. Anderson and B. Andrew Kugler for their assistance, 
guidance and encouragement throughout the project. 




• 



iv 



• 



TABLE OF CONTENTS 



Page. 

PREFACE iii 

LIST OF FIGURES vii 

CHAPTER 1 INTRODUCTION 1-1 

CHAPTER 2 BARRIER NOISE REDUCTION CONCEPTS 2-1 

2-1 Barrier Diffraction and Attenuation 2-1 

2-2 Barrier Transmission 2-7 

2-3 Barrier Reflections 2-9 

2-4 Multiple Shielding Effects 2-13 

2-5 Ground Effects 2-13 

2-6 Barrier Insertion Loss 2-15 

CHAPTER 3 BARRIER DESIGN CONSIDERATIONS 3-1 

3-1 Design Goals 3-3 

3-2 Acoustical Considerations 3-9 

3-3 Safety Considerations 3-20 

3-4 Maintenance Considerations 3-24 

3-5 Aesthetics 3-29 

3-6 Materials and Designs 3-41 

3-6.1 Concrete Barriers 3-46, 

3-6.2 Concrete Masonry Unit Walls 3-48 

3-6.3 Steel Barriers 3-50 

3-6.4 Wood Barriers 3-51 

3-6.5 Earth Berms 3-52 

3-6.6 Noise Barriers for Elevated Structures ... 3-55 

3-6.7 Absorption Treatments for Noise Barriers . 3-55 

3-6.8 Other Materials 3-57 

3-7 Costs 3-58 

3-8 Community Participation in the Barrier Design 

Process 3-62 



TABLE OF CONTENTS (cont'd) 



CHAPTER 4 



BARRIER DESIGN PROCEDURE, 



4-1 Step 1: 



4-2 
4-3 
4-4 
4-5 
4-6 
4-7 
4-8 
4-9 



Step 2 
Step 3 
Step 4 
Step 5 
Step 6 
Step 7 
Step 8 
Step 9 



Determine Noise Reduction Design 

Goals 

Define Site Characteristics 

Determine Geometrical Alternatives 

Identify Additional Barrier Treatments, 

Select Design Options 

Define Cost Factors 

Assess Functional Characteristics , 

Select Barrier , , 

Design Barrier 



Page 
4-1 



4-4 

4-10 

4-18 

4-35 

4-50 

4-66 

4-77 

4-80 

4-80 



CHAPTER 5 BARRIER DESIGN EXAMPLES 5-1 



5-1 
5-2 

5-3 

APPENDICES 
A. 
B. 



C. 

D. 

REFERENCES 



Basic Example of Barrier Design 

Parallel Barrier Example 

Example of Variation in Highway Configuration.. 



Reference Drawings for Walls and Berms 

Reference Drawings for Barriers on Elevated 
Structures 

Reference Drawings for Absorption Treatments 

Design Examples for Existing Noise Barriers 



5-1 

5-11 
5-15 



VI 



LIST OF FIGURES 



Page 



FIGURE 2-1 Alteration of Noise Paths by a Barrier 2-2 

2-2 Barrier Diffraction 2-2 

2-3 Illustration of Path Length Difference 2-4 

2-4 Barrier Attenuation for a Line of Incoherent 

Poi nt Sources 2-4 

2-5 Short-Circuit of Barrier Around Ends and 

Through Openings 2-6 

2-6 Multiple Sound Reflections for a Double-Walled 

Highway 2-10 

3-1 Barrier Design Process Flow Chart 3-2 

3-2 Barrier Noise Reduction Relationships 3-8 

3-3 Barrier Attenuation as a Function of Barrier 

Height 3-11 

3-4 Use of Elevated Terrain to Achieve Greater 

Attenuation with Lower Walls 3-12 

3-5 Illustration of Loss of Attenuation with 

Short Barriers 3-14 

3-6 Use of Local Features to Achieve an "Infinite" 

Barrier 3-15 

3-7 Use of Short Segments Wrapped Around the 

Receiver to Achieve an "Infinite" Barrier 3-15 

3-8 Critical Receiver Considerations 3-17 



Vll 



LIST OF FIGURES (cont'd) 

Page 

FIGURE 

3-9 Use of Safety Barriers 3-21 

3-10 Barrier Location for General Conditions on 

Freeways, Expressways and Highways 3-23 

3-11 Barrier Design Safety Considerations 3-25 

3-12 Maintenance Considerations Concerning Landscap- 
ing 3-27 

3-13 Providing Access for Barrier Maintenance 3-28 

3-14 Spatial Relationship of Barrier to Adjoining 

Land Use 3-30 

3-15 Landscaping can be Visually Pleasing to Both 

the Community and the Driver 3-31 

3-16 Use of Landscaping to Improve Barrier Appearance 3-32 

3-17 Relating Barrier Design to Architectural Elements 

in the Community 3-34 

3-18 Relating Barrier Design to Other Highway 

El ements 3-35 

3-19 Visual Considerations in Barrier Design.. 3-36 

3-20 Varying the Visual Form 3-38 

3-21 Connecting Different Height Walls to Vary Visual 

Form 3-39 

3-22 Use of Berm to Connect Walls and Add Variety 3-40 

3-23 Use of Earth Mound to Termi nate Wall 3-42 



Vlll 



LIST OF FIGURES (cont'd) 

Pa^e 

FIGURE 

3-24 Alternate Means of Terminating Barrier Walls 3-43 

3-25 Use of Planter to Terminate Wall (in protected 

areas only) 3-44 

3-26 Alternate Block Wall Patterns 3-49 

3-27 Alternate Approaches to Berm Construction 3-53 

3-28 Wall and Berm Combined to Create More Height 

in Limited Right-of-Way 3-54 

3-29 Construction Costs for Various Barriers 3-60 

3-30 Construction Costs for Barriers with Additional 

Treatments 3-61 

4-1 Receiver/Highway Distance Relationships 4-6 

4-2 Design Goal Worksheet 4-7 

4-3 Ground Effect Attenuation 4-9 

4-4 Safety Factors for On and Off Ramps 4-11 

4-5 Example of Safety Considerations for On and Off 

Ramps 4-12 

4-6 Safety Factors for Ramp Intersections 4-13 

4-7 Example of Safety Considerations for Ramp 

Intersections 4-15 

4-8 Safety Factors for Intersecting Roads (based on 

Figure 20-1 [a] , Ref. 4-2) 4-16 

4-9 Example of Safety Considerations for Intersect- 
ing Roads 4-17 



IX 



LIST OF FIGURES (cont'd) 

Page 

FIGURE 

4-10 Illustration of Barrier Parameters 4-19 

4-11 Definition of Barrier Parameters 4-20 

4-12 Overview of Barrier Nomograph 4-22 

4-13 Nomograph for Determining Barrier Attenuation... 4-23 

4-14 Barrier Attenuation Example 4-25 

4-1 5 Use of Barrier Nomograph 4-26 

4-16 Use of Nomograph for Trial 4 Foot Barrier.. 4-29 

4-17 Total Barrier Attenuation as a Function of Car 

vs. Truck Attenuation 4-31 

4-18 Use of Nomograph for Trial 6 Foot Barrier 4-33 

4-19 Nomograph for Determining the Effects of Parallel 

Barriers 4-37 

4-20 Example of Cross Section Through Parallel 

Barrier Configuration 4-40 

4-21 Use of the Parallel Barrier Nomograph 4-42 

4-22 Grid to Determine ABAR for Receivers in Region 

II 4-44 

4-23 Use of Grid to Determine ABAR 4-45 

4-24 Effects of Barrier Reflections for Receivers 

in Region III (H N < H R < H p ) 4-48 



X 



LIST OF FIGURES (cont'd) 



Page 



FIGURE 



4-25 Use of Nomograph to Determine Benefits of 

Absorptive Treatments 4-49 

4-26 Design Option Worksheet 4-51 

4-27 Materials for Use in Barrier Designs 4-52 

4-28 Effect of Barrier Openings on TL 4-57 

4-29 Noise Reduction of a Barrier as a Function of 

Its Transmission Loss 4-58 

4-30 Approximate Right-of-Way Necessary for Berm 

Construction 4-61 

4-31 Index to Reference Drawings 4-62 

4-32 Design Code Format 4-65 

4-33 Use of Design Option Worksheet 4-67 

4-34 Cost Factor Worksheet 4-68 

4-35 Grid to Determine Barrier Cost Factor 4-70 

4-36 Use of Grid to Determine Cost Factor 4-72 

4-37 Safety Barri er Cost Factors 4-73 

4-38 Major Cities Cost Index Relationships 4-75 

4-39 Cost Factor Worksheet 4-76 

4-40 Design Evaluation Worksheet 4-78 

4-41 Use of Design Evaluation Worksheet 4-81 



XI 



LIST OF FIGURES (cont'd) 

Page 

FIGURE 

5-1 Sample Highway/ Community Scenario 5-2 

5-2 Use of Design Goal Worksheet 5-4 

5-3 Cross Section Through Receivers 3 and 4 

(Station 1 00) 5-5 

5-4 Use of Nomograph for Trial 14 Foot Barrier 5-6 

5-5 Use of Nomograph for Trial 17 Foot Barrier 5-8 

5-6 Possible Barrier Dimensions 5-9 

5-7 Design Option Worksheet for Basic Example 5-12 

5-8 Cost Factor Worksheet for Basic Example 5-13 

5-9 Design Evaluation Worksheet for Basic Example... 5-14 

5-10 Parallel Barrier Example 5-16 

5-11 Design Option Worksheet for Absorptive Barrier 

Designs. 5-17 

5-12 Cost Factor Worksheet for Absorptive Barrier 

Designs 5-18 

5-13 Roadway and Barrier Profiles 5-20 

5-14 Alternate Approaches to Connecting 13 and 17 

Foot Barrier Walls 5-21 



Xll 



NOISE BARRIER DESIGN HANDBOOK 

CHAPTER 1 
INTRODUCTION 

In recent years, increasing traffic flow on the nation's 
highways coupled with growing public awareness of environ- 
mental issues have established the need to evaluate the 
noise impact of new or existing highway configurations on 
neighboring communities. When the anticipated or current 
noise exposure exceeds desirable limits, there is both 
community pressure and governmental mandate to take the 
necessary steps to prevent or alleviate the noise problem. 

Depending upon the severity of the problem, and the stage 
in which it is discovered, there are a variety of measures 
that might be taken to reduce highway noise impact. These 
measures are generally related to control of motor vehicle 
noise sources (such as traffic management and enforcement 
of vehicle noise regulations) , modification of the highway 
configuration (such as relocation of the highway or use of 
elevated or depressed sections or noise barriers) , and 
changes in receiver sensitivity (such as sound insulation 
or compatible land-use planning) . Solution of a highway 
noise problem should involve a comprehensive analysis of 
all available options, and selection of those measures which 
in conjunction with one another provide the most desirable 
approach. 



1-1 



This handbook deals with just one of these noise abatement 
measures, the use of noise barriers. Because of the wide- 
spread noise impact from existing facilities throughout the 
country, and the practical and cost constraints often imposed 
on projected facilities, the use of noise barriers is perhaps 
the most frequent method for controlling highway noise. Indeed, 
construction of noise barriers has increased dramatically in 
recent years , with projected construction showing even greater 
increases. 

This handbook is intended to be a tool for use by the highway 
designer to aid in the design of noise abatement barriers. 
While it provides a means of defining the geometric configura- 
tion of a barrier to produce a desired noise reduction, it 
goes beyond that by providing a design evaluation and selec- 
tion procedure in which specific barriers are detailed, and 
then evaluated in terms of cost, acoustical characteristics, 
and non-acoustical characteristics (such as durability, ease 
of maintenance, safety, aesthetics and community acceptance) . 
This handbook thus guides the designer in the preparation of a 
design which he believes will be accepted by the community and 
perform as desired both acoustically and non-acoustically , for 
reasonable cost. 

As described in this handbook, the term "noise barrier" 
includes vertical walls, earth berms, and combinations of 
the two. Of course, the lip of an elevated highway or the 
top of the cut of a depressed highway may also serve as a 
noise barrier. Although these are not specifically addressed 
herein, the information that follows may be applied as appro- 
priate to the evaluation of these configurations as barrier 
design alternatives. 



1-2 



Chapter 2 provides a discussion of barrier noise reduc- 
tion concepts. Chapter 3 describes various acoustical and 
non-acoustical factors which must be considered in the design 
of a noise barrier, and provides much of the background for 
the design procedure contained in Chapter 4. The design pro- 
cedure is a step-by-step process in which alternative barrier 
designs are developed and evaluated, followed by selection of 
an "optimum" barrier for the site under consideration. Chapter 
5 provides examples of the design procedure. Appendices 
A, B and C contain reference drawings of noise barriers 
constructed of different materials and treatments. Finally, 
in Appendix D the design procedure of Chapter 4 is applied 
to five existing barriers, to further illustrate the design 
steps and the types of results attainable. 

This handbook should be used in conjunction with other tools 
available to the highway designer for predicting noise ex- 
posure, defining criteria, assessing noise impact, and describ- 
ing other means of noise control. In addition, for those 
interested in gaining a better understanding of the concepts 
underlying barrier design, four companion technical reports 
have been prepared. "Noise Barrier Attenuation: Theory and 
Field Experience" (Reference 1-1) contains a detailed dis- 
cussion of the development of barrier attenuation theory, and 
the various predictive methodologies which have developed from 
the theory. Included also are the results of a field evaluation 
study involving ten barriers located across the country. 
Finally, the volume contains a comparison of barrier attenuation 
predictions with state highway department measurement experiences 



1-3 



"Noise Barrier Catalogue" (Reference 1-2) documents existing 
barriers located throughout the United States in terms of 
their physical dimensions, acoustical performance, and design 
considerations . 

The remaining two reports are both concerned with the appli- 
cation of absorptive materials on highways to reduce the 
noise exposure resulting from multiple reflections. "A 
Study of Multiple Sound Reflections in Walled Highways 
and Tunnels" (Reference 1-3) discusses an analytical and 
scale-model development of predictive procedures to eval- 
uate the effects of reflected sound energy, and the benefits 
that might accrue from use of absorptive material to reduce 
these reflections. "Catalogue of Sound Absorbing Treatments 
for Highway Structures" (Reference 1-4) documents those 
materials that have been studied for use as sound absorbers 
in the highway situation. 



1-4 



CHAPTER 2 
BARRIER NOISE REDUCTION CONCEPTS 

An understanding of the acoustical principals which govern the 
noise reduction provided by a barrier is essential to the design 
of effective barriers. This chapter discusses the basic concepts 
of barrier noise reduction. 

When no obstacles are present between the roadway and adjoining 
areas, sound travels by a direct path from "sources" on the 
roadway to "receivers" off the roadway, as shown in Figure 2-1. 
Introduction of a barrier between the source and receiver re- 
distributes the sound energy into several paths: a diffracted 
path, over the top of the barrier; a transmitted path, through 
the barrier; and a reflected path, directed away from the 
receiver. These paths are also illustrated in Figure 2-1. 

To properly define the complete effect of installing such a 
noise barrier, the sound energy along each of these paths must 
be taken into account, and compared with the sound energy along 
the original direct path. The contribution along each path will 
be individually discussed in the following sections. 

2-1 Barrier Diffraction and Attenuation 

Consider an infinitely long, infinitely massive noise barrier 
placed between the highway and the receiver. Figure 2-2 illus- 
trates a cross-section through such a configuration. For this 
example, the only way that sound can reach the receiver is by 
bending over the top of the barrier; as shown in the figure, 
the sound reaching the receiver is bent through an angle <j>. 
The bending of sound waves in this manner over an obstacle is 
known as diffraction. The area in which diffraction occurs 



2-1 



• 



Source 



rce t 



Direct Path 



Receiver 



Reflected *^ 
ce • ^=" 



Source 

E 



Ptffl 



. ra cfed 



Transmitted 



~^-^~-f Receiver 



FIGURE 2-1 Alteration of Noise Paths by a 
Barrier. 




Diffracted (bent) 
Path 



• 



Rece I ver 



FIGURE 2-2 Barrier Diffraction 



2-2 



• 



behind the barrier is known as the "shadow zone." The straight 
path from the source over the top of the barrier forms the 
bounday of this zone. 

All receivers located in the shadow zone will experience some 
sound attenuation; the amount of attenuation is directly related 
to the magnitude of the diffraction angle <f> . As <f> increases, 
the barrier attenuation increases. The angle <j> will increase if 
the barrier height increases, or if the source or receiver are 
placed closer to the barrier. Clearly then the barrier atten- 
uation is a function of the geometrical relationship between 
the source, receiver, and barrier. One way of relating these 
parameters to the barrier attenuation is to define the path- 
length difference 6 as shown in Figure 2-3. This parameter is 
the difference in distance that the sound must travel in dif- 
fracting over the top of the barrier rather than passing directly 
through it. 

By representing a highway as a line of incoherent (or unrelated) 
point sources, the relationship between the barrier attenuation 
and the path-length difference 6 can be described as in Figure 
2-4 (Reference 2-1) . (Note that in this figure as well as in 
the remainder of this handbook, the symbol A will be used to 
represent attenuation. When necessary to distinguish barrier 
attenuation from attenuation due to other causes , the symbol 
A B will be used.) The barrier attenuation A B represented in 
Figure 2-4 is in units of dBA, and is applicable to the equiva- 
lent noise level L e g. The equivalent level L eq . is an energy 
average of the A-weighted noise levels occurring over a specified 
period, such as an hour. For highways with moderately high 
vehicle volumes, L 1Q = L + 2 dBA, when there is no shielding. 



2-3 



PATH LENGTH DIFFERENCE 5=A+B-d 




SOURCE 




• 



B 



RECE 



RECEIVER 



BARRIER 



FIGURE 2-3 ILLUSTRATION OF PATH LENGTH DIFFERENCE. 



25 



< 

CO 

"O 



2 20 

CO 

< 



O 15h 

< 

D 



LLi 

H 
I- 
< 

CC 

LLI 

o: 
< 

CO 



10 - 




0.05 



KURZE-ANDERSON 
LINE SOURCE CURVE 
(REFERENCE 2-1). 



ADJUSTED TO PROVIDE' 
A MAXIMUM OF 20 dB 
ATTENUATION 



J L 



0.1 0.2 0.5 1 2 5 10 

PATH LENGTH DIFFERENCE 5 IN FEET 



20 



• 



50 



FIGURE 2-4 BARRIER ATTENUATION FOR A LINE OF INCOHERENT 
POINT SOURCES. 



2-4 



♦ 



The attenuation of noise described in terms of L-, will be some- 
what higher than for L eq because L 1Q levels result from traffic on 

a smaller section of roadway than L levels; the barrier is more 

eq 

effective on this smaller section than on larger sections. However, 

for most highway situations the difference between L, A and L 

10 eq 

attenuation will be within 1 dB, and therefore Figure 2-4 is appro- 
priate (if not slightly conservative) for L, n levels as well as 

L „ levels, 
eq 

The curve in Figure 2-4 (with maximum attenuation of 20 dB) has 
been converted to nomograph form (Reference 2-2) for ease of use, 
and is included as part of the design procedure of Chapter 4. 

Note that in comparison with the attenuation prediction metho- 
dologies incorporated within the various analytical procedures 
currently available, the curve in Figure 2-4 and the nomograph 
in Chapter 4 provide attenuation values that are in good agree- 
ment with the predictions of the computer program of the Trans- 
portation System Center (Reference 2-3 / hereinafter referred to 
as TSC) , with the exception that TSC permits attenuation values 
higher than 20 dB. The methodology in NCHRP Reports 117 and 144 
(References 2-4 and 2-5, hereinafter referred to as 117/144) 
provides comparable attenuations for car sources, but truncates 
the attenuation at 15 dB. For trucks, 3 dB is added to the car 
attenuation. 

In the preceding discussion it was assumed that the barrier was 
"infinite"; i.e., long enough to shield the receiver from all 
sound sources up and down the highway. For short barriers, the 
attenuation can be seriously limited by the sound from sections 
of highway beyond the barrier's ends, which are unshielded from 
the receiver, as shown in Figure 2-5. Similarly, when there are 



2-5 



• 



if) 
en 

c 



0) 

> 

o 

0) 



\ 



\ 



s 



/ 



™ / 



< 




CD 
CL 

o 

.c 
en 

3 

o 

S- 



-a 

c: 

fD 

i/i 
-a 

c 

UJ 

-a 

E 
3 
O 

s- 

<c 

s_ 
a) 
•i— 

s_ 
s_ 

03 
CO 



o 



(J 

S_ 
•i — 

o 

I 
+-> 

i- 

o 

t/0 



LO 
CO 



• 



on 

CI3 



• 



2-6 



large gaps in the barrier (to permit access, for example), 
sound from the unshielded section of highway adjacent to 
the gap can greatly compromise barrier attenuation, es- 
pecially for those receivers close to the opening. The 
amount of shielding provided by a finite barrier can be 
related to the angle a subtended by the barrier (or by a 
section of a barrier) . By summing the sound energy con- 
tributions from both shielded and unshielded sections of 
highway, the net attenuation due to the barrier can be 
determined as a function of barrier subtended angle. 
The nomograph in Chapter 4 permits evaluation of the barrier 
attenuation in terms of this angle. 

2-2 Barrier Transmission 

In addition to the sound that travels over the top of the 
barrier to reach the receiver, sound can travel through the 
barrier itself. The amount of "transmission" through the 
barrier depends upon factors relating to the barrier material 
(such as its weight, and stiffness and lost factors) , the 
angle of incidence of the sound, and the frequency spectrum 
of the sound. One way of rating a material's ability to 
transmit noise is by the use of a quantity known as the trans- 
mission loss, TL. The TL is related to the ratio of the inci- 
dent noise energy to the transmitted noise energy. 

For spectra typical of highway noise sources, transmission 
loss values can be determined for specific types of materials, 
Chapter 4 provides TL values for a wide range of materials 
commonly used as noise barriers. Typically, the transmission 
loss improves with increasing surface weight of the material. 



2-7 



The noise reduction provided by a barrier can be severely 
compromised if the transmission loss of the material permits 
too much noise to pass through the barrier. As a general rule, 
if the transmission loss is at least 10 dB above the attenuation 
resulting from diffraction over the top of the barrier, the 
barrier noise reduction will not be significantly affected by 
transmission through the barrier (less than 0.5 dB) . For many 
common materials used in barrier construction, such as concrete 
and masonry blocks, transmission loss values are usually more 
than adequate. For less massive materials such as steel, aluminum 
and wood, transmission loss values may not be adequate, particularly 
for those cases where large attenuations are required. 

Even if a barrier material is massive enough to prevent 
significant sound transmission, the barrier noise reduction 
can be severely compromised if there are holes or openings 
in the barrier. For large openings, sound energy incident 
on the barrier will be directly transmitted through the 
opening to the receiver. When the opening is small an 
additional phenomenon occurs: upon striking the barrier 
wall the sound pressure will increase resulting in an am- 
plification of the transmitted sound to the receiver. Thus, 
the presence of openings or holes may seriously degrade the 
noise reduction provided by otherwise effective barriers. 

Note that the procedure in Chapter 4 provides details of 
the effects of inadequate transmission loss properties on 
the barrier noise reduction. 



• 



2-8 



t 



• 



2-3 Barrier Reflections 

As shown in Figure 2-1, sound energy can be reflected by a 
barrier wall. For the configuration shown in that figure, 
the reflected energy does not affect the receiver, but may 
affect receivers located to the left of the highway. However 
the increase in noise level for these receivers would be less 
than 3 dB, because this single reflection can at most double 
the sound energy. 

The situation is entirely different, however, when a double 
barrier situation is involved (refer to Figure 2-6) . In 
addition to the energy that reaches the receiver by diffrac- 
tion over the top of the barrier, if the barrier walls are 
reflective additional sound energy can reach the receiver 

by a reflection from the right wall as illustrated in the 
figure. This energy can be conceived of as coming from an 
image source i-| , located to the right of the barrier. 
Similarly, there is still another image source, i 2 , which 
results from the reflection of sound energy first from the 
barrier on the left and then the barrier on the right, and 
so on. Note that the same principles apply when there is a 
vertical retaining wall opposite a noise barrier; similarly, 
in a deep vertical cut the opposite walls will create multiple 
reflections. 

The number of image sources which contribute significantly 
to the total sound level at a receiver is a function of 
receiver height. For example, if the receiver cannot see 
the far barrier, then an infinite number of image sources 
contribute to the total level because there are an infinite 



2-9 



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2-10 



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number of reflections. As the height of the receiver increases, 
the number of contributing image sources decreases, and the 
effectiveness of the near barrier decreases. Thus each reflec- 
tion becomes relatively less important because the level of 
the source itself increases as the shielding is decreased. As 
the height is further increased, a point is reached where no 
reflections contribute to the level at the receiver. 

One way of evaluating the effect of these multiple reflections 
is to consider the change in barrier attenuation resulting from 
the presence of the second barrier. The presence of the wall 
on the right of the highway will degrade the performance of 
the barrier on the left by an amount which can be called ABAR. 
ABAR is a function of receiver height, barrier height, highway 
width, and receiver distance to roadway. 

However, if the barrier walls are not perfectly reflecting but 
absorb some of the sound energy, the contribution of each re- 
flection is decreased by an amount that depends upon the 
absorptive characteristics of the barrier. The ratio of the 
acoustical energy absorbed by a material to the total energy 
incident upon that material is known as the absorption coeffi- 
cient, usually denoted by the symbol a. For any particular 
material, the absorptive characteristics will be a function of 
frequency. In order to rate the overall absorptive characteris- 
tics of the material, a measure of the average absorption over 
the frequency range of interest is useful. An appropriate 
measure is the Noise Reduction Coefficient, NRC. The Noise 
Reduction Coefficient is the arithmetic average of the absorp- 
tion coefficients in the four octave bands which cover the 
frequency range from approximately 200 to 3000 Hz: 



NRC = \ (a 25Q + a 50Q + a 100Q + a 2QQQ \ 



2-11 



For very hard reflective surfaces, the absorption coefficients 
(and thus NRC) are very small, nearly zero. For materials which 

absorb almost all of the incident energy, the absorption coeffi- Uh 
cients and the corresponding NRC are nearly one. 

Although a serious degradation in barrier performance may result 
for the double barrier situation, use of materials with' high NRC 
values will usually recover all of the lost noise reduction. 
A methodology for determining ABAR for hard reflective walls, 
as well as for walls lined with highly absorptive materials, 
is provided in Chapter 4. 

It should be mentioned that the use of barrier walls with 
sloped sides (forming angles of greater than 10 - 15 degrees 
from the vertical) will also generally eliminate multiple 
reflections. Use of earth berms is particularly appropriate 
to accomplish this. Sloped barrier walls will require more 
material to achieve a desired height than a vertical wall, 
while berms will require greater right-of-way than a thin 
wall. 

Note that the use of absorptive materials on single barrier 
walls generally provides no benefit. For diffraction angles 
greater than 45°, absorptive materials can influence the sound 
that is diffracted over the top of the barrier. However, in 
most highway situations it is rare to find a configuration in 
which the diffraction angle will approach that magnitude. For 
angles less than 45° use of absorptive materials is of little 
advantage in reducing noise levels. 



2-12 



2-4 Multiple Shielding Effects 

The effects of sound diffraction over more than one barrier 
are not well understood. It is believed that for situations 
in which a barrier is placed between a roadway and rows of 
houses and/or significant stretches of vegetation which shield 
a receiver, the benefits of the barrier attenuation, house 
attenuation, and vegetation shielding may be additive. The 
current noise estimation procedures (TSC and 117/144) use 
this assumption. 

On the other hand, when more than one barrier is placed between 
a roadway and a receiver, the combined effect is not to provide 
significantly greater attenuation than the single barrier. For 
design purposes, the general procedure is to assume the atten- 
uation of the most effective barrier. 

One implication of this is that when a barrier exists between 
the roadway and receiver, and it is desired to construct a 
second barrier to provide additional noise reduction, the 
attenuation provided by the first barrier is lost and only 
the attenuation of the second will be useful to reduce noise 
levels. 

2-5 Ground Effects 

Consider again the direct path of sound from the source to 
receiver as illustrated in Figure 2-1 in the absence of any 
obstacles. For sources and receivers located close to the 
ground, in addition to this direct path sound energy may 
reach the receiver by reflecting off the ground. When the 
terrain is relatively hard and flat, such a reflection will 



2-13 



add to the noise from the direct path to increase the level 
at the receiver. However, when the ground is soft, there 
may be a phase reversal upon reflection such that the noise 
from the ground reflection path will destructively interfere 
with the noise from the direct path resulting in a reduction 
in level at the receiver which could be quite significant. 

This reduction in level, known as ground-effect attenuation, 
is in excess of the 3 dB per doubling of distance propagation 
loss for a line source of noise and occurs only above soft 
absorptive ground (such as normal earth and most ground with 
vegetation) . Over hard ground (such as concrete, stone and 
very hard-packed earth) these ground effects do not occur. 
These effects are most apparent for receivers on the ground 
floor, and decrease rapidly as receiver height above ground 
increases. 

While ground absorption effects are not completely understood, 
it is generally believed that these effects account for the 
4.5 dB per doubling of distance propagation loss observed 
over soft ground, as compared to the 3 dB propagation loss 
observed over hard ground. The implication with regard to 
barrier design is that placement of a barrier over soft ground 
between source and receiver will re-direct the sound over the 
top of the barrier, thus destroying the ground reflection and 
the additional 1.5 dB per doubling of distance attenuation. 
Thus, the barrier must be designed to provide more reduction 
than would otherwise be necessary, to compensate for the lost 
ground effects over absorptive ground. 



2-14 



2-6 Barrier Insertion Loss 

The noise level observed at a particular location after con- 
struction of a noise barrier will depend on all of the factors 
discussed above. It is useful to define the concept of barrier 
insertion loss (IL) as the difference in noise level measured 
at a receiver location before and after construction of the 
barrier. 

This insertion loss is a function of the following: 



IL = f ( A B , TL, ABAR, A g , A^ (2-2) 



where 



A_. = barrier attenuation resulting from 
a 

diffraction over the barrier top 

TL = transmission loss through the barrier 

ABAR = change in barrier attenuation resulting 
from multiple reflections from double 
barriers 



A = shielding attenuation from other barriers 
between highway and receiver 



A^ = attenuation from ground effects 



The barrier attenuation A B/ transmission loss TL, and change 
in barrier attenuation ABAR combine to give a net noise re- 
duction, NR, for the barrier. That is, 



2-15 



NR = f ( A B , TL, A BAR J . (2-3) 

construction of the barrier, the receiver may have been 
shielded by another barrier. Alternatively ground effects may 

influenced the noise level at the receiver. (Typically 
30th effects would not have occurred together, since the other 
barrier would have destroyed the ground effects.) Thus the 

nsertion loss at the receiver due to construction of the 
barrier would be 

IL = NR - max ( A_, &„] (2-4) 



(V a g) 



since the shielding due to the other barrier A g or the ground 
sts losses Aq, if originally present, would be lost upon 
truction of the barrier. Note that the notation max(a,b) 

means that the larger value of a and b is to be used in the 

equation. Also note that A s does not include the shielding 

provided by rows of houses or vegetation. 

It should be clear from the above equation and discussion that 
determination of the effects of a noise barrier solely on the 
basis of diffraction over the top of the barrier will not pro- 
vide a true picture of the net benefit of the barrier. 



2-16 



CHAPTER 3 
BARRIER DESIGN CONSIDERATIONS 

The previous chapter addressed the basic physical principles 
underlying barrier noise reduction. In this chapter, these 
basic concepts are applied to the design process to give the 
highway designer an understanding of the various factors that 
must be considered to build a barrier that is acoustically 
effective; i.e., a barrier which provides the required inser- 
tion loss without being "overdesigned. " This chapter also 
provides information about the factors to be considered in 
barrier design that are related to non-acoustical features of 
barriers, such as maintenance, aesthetics, safety, construction, 
and costs. Also considered in this chapter is the role of 
community participation in barrier design. 

Figure 3-1 shows a flow chart of the major elements of the 
barrier design process. As shown on the figure, the noise 
reduction goals influence the acoustical considerations, 
which in conjunction with the non-acoustical considerations 
determine various barrier design options. These options are 
then evaluated and a single design is selected, optimized and 
implemented. Input from the community is incorporated through- 
out the process. 

For reference, the numbers in italics in each box correspond 
to the section in this chapter which addresses the particular 
subject indicated. The encircled numbers refer to the appro- 
priate steps in the barrier design procedure in Chapter 4. 



3-1 



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3-2 



Much of the material presented in this chapter thus provides 
background and rationale for this design procedure. In apply- 
ing the procedure in Chapter 4, then, knowledge of the con- 
siderations discussed in this chapter will be invaluable. 



3-1 Design Goals 

As a starting point in the design process, design goals should 
be set. These may take the form of a desired uniform reduction 
of X dB for a particular community, or, more likely, individual 
receiver levels would be defined and a desired criterion level 
selected. The design goal insertion loss would then be the 
difference between the present level and the criterion level 
for each receiver (selection of "critical receivers" will be 
discussed below; these are receivers picked so that when the 
design goals are achieved for their location, they are achieved 
for the entire community of interest.) Although this design 
goal may be modified during the course of the design process, 
it is extremely useful to identify early a target for which 
to aim. 

As discussed in Chapter 2, the insertion loss provided by a 
barrier depends upon the diffraction of sound over the top 
and flanking around the sides of the barrier, transmission 
of sound through the barrier, multiple reflections caused by 
double barriers, and the potential loss of ground effect 
attenuation or the attenuation of other shielding elements 



3-3 



between the roadway and receiver. The design goal insertion 
loss may then be expressed as follows: 

Design goal IL = L (before) - L (criterion) 

= NR - max(A s , A Q ) (3-1) 

where 



NR 



= f(A B , TL, ABAR) (3-2) 



In this equation L (before) and L (criterion) are expressed as 
either L^_q or L ea levels in dBA. The noise reduction NR is 
the net barrier benefit resulting from diffraction, transmission, 
and double barrier effects. In order to achieve the desired 
insertion loss, the barrier must therefore be designed to achieve 
a design goal noise reduction defined as follows: 

Design goal NR = L (before) - L (criterion) + 

max^Ag, A Q \ (3-3) 

With proper selection of barrier material and construction tech- 
niques, transmission through the barrier should not significantly 
compromise barrier performance. Further, if parallel barriers 
are not to be constructed, then the design goal NR will effec- 
tively become the design goal for the barrier attenuation A . 

In order to determine the various parameters in the above 
equation, the highway designer may use one of the methods 
available, that is 117/144 or TSC . Alternatively, for 
existing highways, some of these parameters may be deter- 
mined by actual field measurements at particular locations 
of interest. As an added benefit, use of field measurements to 



3-4 



determine L (before) provides useful documentation of pre-barrier 
conditions, and can be used to validate the analytical predic- 
tions. 

Even if analytical methods alone are used to determine noise 
levels for the "before" case, use of field measurements to 
determine possible ground absorption effects, A_, would be most 
useful. Such measurements would involve measurement at a typical 
ground level receiver location (5 feet above ground) , with simul- 
taneous measurements at least 20 to 25 feet in the air; the 
difference in level between these two measurements is a good 
measure of the amount of absorption caused by ground effects. 
Note that when field data defining A_ are not available, the 
design curve provided in Chapter 4 may be used. This curve 
is based on a 1.5 dB per doubling of distance (from 50 feet) 
increase, to an arbitrary maximum of 5 dBA. 

Since the attenuation provided by a barrier is critically 
dependent upon the height of the noise source, the design 
goal attenuation for the barrier must be translated into 
a design goal attenuation for sources at different heights. 
Usually, highway noise sources may be grouped into two height 
categories: ground- or zero-foot sources, resulting from 
automobile and light and medium truck tire noise; and eight- 
foot sources, resulting from heavy truck engine and exhaust 
noise. Although not technically correct, for convenience 
in the remainder of this handbook all zero-foot sources will 
be called cars, and all eight-foot sources will be called 
trucks. In Chapter 4, the attenuation provided by a barrier 
for car and truck sources relative to the total attenuation 
of the barrier is defined as a function of the relative car 



3-5 



and truck contributions to the total traffic noise environ- 
ment. From this information the design goal attenuations 
for cars and trucks may be determined from the design goal 
attenuation for the total traffic flow. 

Any barrier which breaks the line of sight between the source 
and receiver will generally provide 5 dBA attenuation. However, 
because of possible loss of ground attenuation, the insertion 
loss of such a barrier is often only 1 or 2 dBA. Further, 
even if a full 5 dB is obtained, this magnitude of noise re- 
duction subjectively does not usually appear to be very 
significant. Thus the wisdom of building a barrier to achieve 
an attenuation of 5 dB should be carefully considered. 

It is usually quite possible to achieve a 10 dB barrier 
attenuation using walls or berms of reasonable height and 
length. An attenuation of 15 dB is more difficult to attain, 
and usually involves fairly high structures, the use of 
materials with high transmission loss characteristics, and 
attention to details of construction to ensure that leaks 
or openings are minimal. The length of such a barrier is 
usually significant. 

To achieve a 20 dBA noise reduction is nearly impossible. 
For the purposes of this handbook, a 20 dBA limit has been 
placed on the attenuation provided from any barrier. If 
the design goal insertion loss exceeds 20 dB (or is much 
greater than 15, for that matter), the highway designer 
should seriously consider the use of other noise reduction 
measures to achieve the desired noise environment, or use of 
a barrier to partially reduce highway noise levels supplemented 
with other measures to jointly achieve desired levels. 



• 



3-6 



As a summary of the magnitude of reduction achievable with 
noise barriers, Figure 3-2 categorizes barrier attenuation 
in 5 dB steps. For comparison purposes, the figure also 
indicates the actual reduction in acoustic energy, and the 
corresponding subjective assessment of this reduction, for 
each attenuation step. Note that a 10 dB reduction in noise 
level is necessary to reduce the loudness by half, even 
though this corresponds to elimination of 90% of the acous- 
tic energy. As can be inferred from the figure, small 
differences in attenuation would not evoke significantly 
different subjective reactions. 

While developing barrier designs to meet design goals, the 
designer will find it a fairly simple matter to evaluate 
the noise reduction benefits, as well as costs, of increas- 
ing barrier height and/or length. It may be appropriate 
therefore, depending upon cost tradeoffs, to build slightly 
better barriers if the extra cost involved is not significant, 

On the other hand, use of other measures to reduce noise 
exposure may turn out to be less costly than construction 
of a barrier of sufficient height and length to meet design 
goals, depending upon specific circumstances and highway- 
community configurations. Thus, application of these other 
measures should not be eliminated from consideration until 
after the highway designer has gone through the procedure 
of Chapter 4 and determined the cost of the noise barrier 
selected. 

The important point here is that although a design goal 
insertion loss is chosen at the start of the design process, 
it may be increased if found to be cost-effective, or 



3-7 



• 



FIGURE 3-2 
BARRIER NOISE REDUCTION RELATIONSHIPS 



Barrier 


Level of 


Reduction 


in 


Reduction in 


Noise Reduction 


Feasibility 
Simple 


Acol 


istic Energy 
68% 


Loudness 


5 dB 


30% 


10 dB 


Attainable 




90% 




50% 


15 dB 


Very Difficult 




97% 




65% 


20 dB 


Nearly Impossible 




99% 




75% 



t 



3-8 



• 



decreased (or the barrier eliminated entirely) , if other 
measures are shown to be more cost-effective. Thus the 
highway designer should remain flexible in his approach 
so that all options are pursued and analyzed. 

A final point is in order. Just as it was important to 
obtain measurements at important receiver locations before 
construction of the barrier to document existing levels, 
it is quite useful to make measurements after barrier 
construction to document actual barrier performance. 
Such measurements will provide a true measure of the 
insertion loss of the barrier. If the barrier has met its 
design goal, these measurements are useful from a community 
relations point of view. If the design has not been success- 
ful, it is important to recognize that fact so that, if 
possible, the problem can be remedied. Even if it is not 
possible to remedy the problem, analysis of the reasons 
that the barrier does not achieve its design insertion loss 
would provide a useful lesson which could be of great benefit 
in the design of future barriers. 

3-2 Acoustical Considerations 

As discussed in Chapter 2, the attenuation of a barrier is 
directly related to the path length difference 6 of the 
diffracted sound over the top of the barrier as compared 
with the direct path from the source to receiver in the 
absence of the barrier. This assumes that the barrier is 
infinitely long, parallel to the roadway, and of constant 
height. How do these concepts translate themselves to the 
real world, and influence the practical design of a barrier? 



3-9 



Consider first the parameters of barrier height and location 
relative to the roadway. At a fixed distance from the road- 
way, increasing the height of the barrier will increase its 
attenuation characteristics. This relationship is non-linear, 
however; for low values of attenuation, increasing the wall 
height a constant amount may provide reasonable increases in 
attenuation. For this situation, it would be very cost- 
effective to increase wall height, because the attenuation 
per foot of height is large. Once the attenuation has in- 
creased substantially, however, increasing the height of the 
wall may provide very little additional benefit in terms of 
increasing attenuation. In this region increasing the height 
of the wall the same amount will provide much less benefit. 
This situation is illustrated in Figure 3-3. Note however 
that despite this non-linear behavior, for rough approximation 
purposes a value of 1/2-dB attenuation per incremental foot 
of height may be used to estimate the approximate height of 
a wall to achieve a desired attenuation, assuming that a wall 
which just breaks line-of-sight provides 5 dB attenuation. 

For a constant barrier height, moving the wall close to the 
receiver, or close to the source, provides increasing attenua- 
tion. However, in practical design, it may be possible to 
take advantage of local terrain conditions to find a barrier 
location which can benefit from higher elevations. This 
situation is illustrated in Figure 3-4 in which a short barrier 
wall placed on a hilly terrain combines to provide more attenu- 
ation than a higher (and therefore more expensive) wall located 
closer to the roadway. 



3-10 



20 



15 - 



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CO 



10 - 



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03 

CO 



TRUCKS « 
CARS -•■ 



BARRIER 

n 
H 



SECTION 



• RECEIVER 



50' 



200' 



CAR 
ATTENUATION 




TRUCK ATTENUATION 



■ 0.5 dBA ATTENUATION 

per FOOT of 
BARRIER HEIGHT 



10 15 

Barrier Height, Feet 



20 



25 



FIGURE 3-3 Barrier Attenuation as a Function of Barrier Height 



3-11 



• 



This 12' wall provides greater 
attenuation than the 20' wall. 



20' 



vnuNittr - \>> >>>>>>>* 




• 



FIGURE 3-4 Use of Elevated Terrain to Achieve Greater 
Attenuation with Lower Walls. 



3-'12 



• 



In practice, one does not build infinite barriers. Yet the 
need for barriers which subtend large angles from observers 
is a real one. Consider the situation illustrated in Figure 
3-5 in which a barrier of "infinite" length, with a subtended 
angle of 180°, would provide an attenuation of 16 dB. The 
same barrier subtending an angle of 160° will provide only 11 
dB attenuation. Note that for a receiver 500 feet from the 
roadway, a barrier which subtends an angle of 160° would be 
more than a mile long; still, this barrier has been degraded 
by 5 dB because it is too short. How can this situation be 
remedied? There are basically two ways. One is to take ad- 
vantage of natural terrain conditions and the presence of 
structures to provide the necessary "infinite" length, as 
shown in Figure 3-6. The other method, which may have to 
be used if terrain and structures do not provide the necessary 
shielding at the end of the barrier, is to bend the barrier 
back toward the community to achieve a larger subtended angle 
through much reduced length, as shown in Figure 3-7. 

Until now, the discussion has been directed toward the height, 
location, and length considerations necessary to achieve a 
desired insertion loss for one particular receiver. In the 
typical situation, however, there may be many receivers for 
whom the barrier is being designed to protect. These are 
receivers who are or will be exposed to noise levels higher 
than criterion levels, as determined by field measurements 
or analytical procedures (resulting perhaps in noise exposure 
contours) . Since it clearly is impractical to evaluate the 
various design options for every receiver of interest, it is 
useful to identify a few "critical receivers" for whom selec- 
tion of proper barrier parameters is most crucial. Concep- 
tually, these receivers would be picked so that a barrier 



3-13 



-\ 



• 



11 dB 




1.6 dB 



160° barrier provides 11 dB attenuation, 

"Infinite" barrier provides 16 dB 

attenuation. 



• 



FIGURE 3-5 Illustration of Loss of Attenuation with Short 
Barriers. 



3-14 



• 



-\ 




FIGURE 3-6 Use of Local Features to Achieve an "Infinite" 
Barrier. 



-\ 





FIGURE 3-7 



Use of Short Segments Wrapped Around the Receiver 
to Achieve an "Infinite" Barrier. 



3-15 



design which achieves the desired noise reduction goals for 
these receivers would also meet or exceed desired goals for 
all other receivers of interest. Clearly, the smaller the 
number of critical receivers necessary to satisfy these re- 
quirements the better. 

Explicit guidelines cannot be given for the selection of 
critical receivers. Typically, however, the highest noise 
levels and therefore the greatest noise reduction require- 
ments will apply to the closest receivers. Selection of 
barrier location and height will then be dictated by the 
noise reduction requirements of these receivers. Usually 
the noise level will drop off with distance from the high- 
way at a faster rate than the decrease in barrier attenuation 
with distance from the barrier. Thus, if the noise level 
at the closest receiver is reduced to design levels, the 
noise level at the farthest receiver of interest will also 
be within desired limits. However, if the barrier protecting 
the close-in receiver is significantly less than infinite, 
the length of barrier required to protect the close-in 
receiver may be insufficient for the farthest out receiver. 
Thus the close-in receiver may determine the barrier height 
while the far-out receiver may determine its length. 

Of course there rarely is the situation of a single column of 
receivers extending out from the roadway. The considerations 
described above must be extrapolated to an entire community 
area. Consider the simplified situation shown in Figure 3-8. 
It is the receivers on the right of the community who will 
determine the height and length requirements for the barrier 
in that vicinity extending to the right, while the receivers 
on the left will control the barrier dimensions for the left 



• 



3-16 



• 



t\ 



I 



f 



*=- 




THESE RECEIVERS 
DETERMINE 
BARRIER HEIGHT 




THESE RECEIVERS 
DETERMINE 
BARRIER LENGTH 



THESE RECEIVERS DETERMINE 
BARRIER DIMENSIONS TO THE 
LEFT 



THESE RECEIVERS DETERMINE 
BARRIER DIMENSIONS TO THE 
RIGHT 



FIGURE 3-8 Critical Receiver Considerations 



3-17 



i 



portion of the barrier. Note that there is no requirement 
that a barrier have constant height throughout its entire 
length. The necessary height will vary according to the 
location and height of the various receivers, as well as 
changes in alignment, grade, and cross-section configuration 
of the highway. When a community extends for a considerable 
distance along the highway, it may be appropriate to divide 
the route into sections, and effectively design separate 
barriers for each section, with different heights along each. 
Knowledge of the highway alignment and elevation will provide 
guidance as to whether adjoining sections of receivers will 
achieve sufficient benefit from the section of barrier upstream 
or downstream, which might be lower than the height of the 
barrier immediately between them and the roadway. 

Because of these complexities in highway and community 
configurations, as well as variations in terrain features, 
it is often advisable to make use of available computer 
programs (such as TSC) to properly evaluate the effects 
of these various factors so that the attenuation provided 
by a barrier of varying height can be determined for an 
array of observers. Of course, such a procedure could become 
very time consuming and costly if many different barrier 
design options are evaluated in this manner. Alternatively, 
a uniform height barrier may be used along all sections of 
the road, with simplifying assumptions made about the highway- 
community configuration. For purposes of comparing the costs 
and non-acoustical characteristics of different barrier designs, 
use of single height barriers is certainly adequate. After 
a specific design is chosen, it can be refined and optimized 
by computer into different height sections. This approach 
will be discussed in greater detail in Chapter 4. 



3-1 



As indicated in Chapter 2, the performance of a barrier 
can be seriously limited by transmission through the 
barrier and by reflected sound energy due to the presence 
of a second barrier on the other side of the highway. 
Selection of barrier material with sufficiently high trans- 
mission loss characteristics in terms of both the material 
itself and the absence of holes or openings in the material 
is quite important. Similarly selection of sound absorptive 
material treatments for barrier application also deserves 
serious consideration. 

Another way that barrier performance can be compromised is 
the presence of large gaps or discontinuities in the design 
to accommodate pedestrian access, cross-street penetration, 
or access to the roadway for maintenance purposes. Wherever 
possible, the effects of these gaps should be minimized by 
overlapping sections of barrier, providing a tight-fitting 
access door, or bending back the barrier ends toward the 
community to shield nearby receivers. 

Conversely, it is possible to "overdesign" a noise barrier. 
For situations in which the design goal is not large (under 
10 dB for example) , selection of material with unnecessarily 
high transmission loss properties and meeting unnecessarily 
rigid specifications concerning openings may place a high 
price tag on the barrier that is unwarranted. 

Serious overprediction of "before" noise levels at critical 
receivers would also result in an overdesigned noise barrier. 
One reason that this might occur is the failure to categorize 
traffic flow into automobiles, medium trucks and heavy trucks, 



3-19 



Use of only two categories (i.e., including medium trucks with 
heavy trucks) would often overpredict the noise level. Because 
of the different pecularities inherent in each of the analytical 
prediction methodologies that may be used, it is strongly rec- 
commended that the highway designer have a clear understanding 
of the strengths and weaknesses of the particular methodology 
he is using so that he knows how much faith to place in the 
estimated noise levels at receivers. 

3-3 Safety Considerations 

A number of safety factors must be considered when designing 
noise barriers. Clearly, a barrier should not be installed 
where it will present a hazard to safety. 

From a safety standpoint, it is desirable to locate a noise 
barrier beyond the recovery zone from the traveled way. 
Where a roadside obstacle such as a noise barrier is within 
thirty feet of the traveled way, a traffic barrier may be 
warranted (Reference 3-1) . However, it is recognized that 
this is frequently impractical in conditions where walls 
are added within an existing freeway right-of-way. In 
existing projects where desirable clearance may not be ob- 
tainable, such as on elevated structures, it is generally 
desirable to have a safety barrier used either in front of, 
or as part of the acoustical barrier. (See Figure 3-9.) 
In a crash situation, the vehicles tend to protrude over 
the top of the safety barrier, therefore the noise barrier 
wall may be subject to damage even with the inclusion of 
a crash barrier. 



• 



3-20 



Acoustic Barrier 



Edge of Lane 




WHERE AN ACOUSTIC BARRIER IS WITHIN THIRTY 
FEET OF THE TRAVELED WAY, A TRAFFIC BARRIER 
MAY BE WARRANTED 



Safety Barrier Part of Wall 





Safety Barrier 



FIGURE 3-9. USE OF SAFETY BARRIERS 



3-21 



In general, the location of a noise barrier with respect 
to the traveled way will vary with the shoulder width 
required. As indicated in Figure 3-10, the width of the 
shoulder will vary from eight feet to twelve feet, depending 
upon the roadway characteristics. (Note however that for 
elevated structures there should be a minimum of four feet 
from the edge of the traveled way for adequate shy distance.) 
The location of the walls shown in the figure are for general 
conditions; however, each installation should be evaluated 
for traffic safety with special emphasis on alignment and 
sight distance. 

Consideration must be given to safety when locating noise 
barriers in the vicinity of on- and off-ramps, ramp inter- 
sections, and intersecting roadways. A noise barrier should 
not block the line-of-sight between the vehicle on the ramp 
and approaching vehicles on the major roadway. Several 
specific conditions are described in the following. 

For on- and off-ramps the minimum set back of a noise barrier 
is based upon the stopping sight distance, which is a function 
of the design speed and radius of curvature of the ramp. For 
ramp intersections, proper barrier location is set by the 
sight distance corresponding to the time required for a stopped 
vehicle to execute a left-turn maneuver (approximately 7.5 
seconds) . For intersecting roadways, barrier placement is 
determined from stopping sight distance., which depends on 
driver reaction time and deceleration rate. Design charts 
are included in Chapter 4 to assess proper barrier locations 
for these conditions. (Note that barrier termination con- 
siderations are discussed below in Sections 3—4 and 3-5.) 



3-22 



» 



\ 



Travelled way, emergency lane, bike lane, 
sidewalk, and median 






Acoustical 

vertical 

wall 



Standard 

barrier 

wall 



STRUCTURE 



Acoustical 
vertical wall 



ET3' 



Shoulder 
(see table) 



Shoulder 
(see table) 



Traveled way and median 



Acoustical 
vertical wall 



-0 




1 

Berm g 



Varies with foundation requirements for vertical wall 



> 



Type of cross section 


* 
Paved shoulder width - feet 


Right of traffic 


FREEWAYS 


(a) 4 and 6 lanes 

(b) 8 lanes or more 

(c) Separate roadways 

(d) Auxiliary lanes 

(e) Freeway to freeway connections 

(f) Ramps 


10 
10 
10 
10 
10 
8 


ULTIMATE EXPRESSWAYS AND HIGHWAYS WITHOUT ACCESS CONTROL 


Standard 2-lane Highways 

Muitilane Divided Highways: 

(a) Narrow Median with continuous curbs 

(b) 4 and 6 lanes 

(c) 8 lanes 

(d) Separate roadways 


8 

8 
8 
8 
8 



* 10-12 feet where snow storage required. 

FIGURE 3-10 Barrier Location for General Conditions on Freeways, 
Expressways and Highways 



> 



3-23 



Snow removal considerations become a safety factor when the 
melting snow forms ice on the roadway surface. In general, 
the common practice in snow areas is to design highways with 
a minimum shoulder of ten to twelve feet to allow for snow 
storage areas when snow cannot be readily pushed over to 
the side due to the placement of a noise barrier. In this 
situation, it will be necessary for the snow to be first 
plowed off the traveled lanes onto the wider shoulders and, 
following the storm, load the snow into transport vehicles. 
In this case it is important to remove the snow from the 
shoulder as soon as possible to minimize the possibility of 
melting snow blowing onto the roadway at night and freezing. 
The surface treatment of the barrier also has safety impli- 
cations. Protrusions on a barrier near a traffic lane, and 
facings which can become missiles in a crash situation should 
be avoided. See Figure 3-11. 

The previous discussion and illustrations regarding barrier 
safety are intended as general guidelines. Consult references 
3-1, 3-2, and 3-3 and appropriate state design standards for 
applicable criteria. 



3-4 Maintenance Considerations 

Maintenance factors include maintenance of the noise barrier 
itself; maintenance associated with adjoining landscaping; 
replacement of materials damaged by impact; and cleaning the 
barrier. 



3-24 



AVOID LARGE COLUMN 
PROTRUSIONS ON WALL 
ADJACENT TO TRAFFIC 
LANE 



ACCEPTABLE 




M»»ia^^ 



i'^i , ivi , iSvriYiSviS , i'i , i , i , i^''iSviviYi^Vi'iviSviS^ 



jiEnnxon 




^* ijii ii< mv 




AVOID FACING WHICH 
MAY BECOME MISSILES 



FACING SET INTO 
RECESS 



FIGURE 3-11. BARRIER DESIGN SAFETY CONSIDERATIONS 



3-25 



In general, maintenance of barrier materials is less costly 
if unpainted surfaces such as weathering steel, concrete, 
pressure-treated wood, or naturally weathered cedar or red- 
wood are used. It is desirable from a visual and maintenance 
standpoint to use concrete surfaces which are left natural 
such as sandblasted finish and exposed aggreate, or with 
integral color, as opposed to painted surfaces which require 
continual long-term maintenance. 

Maintenance of landscaping associated with the edge of the 
freeway right-of-way will be affected by both the wall place- 
ment and type of landscaping used. In general where the wall 
splits the area to be landscaped, it is desirable to utilize 
low maintenance landscaping on the far side (see Figure 3-12) • 



Providing access to the rear of the wall for maintenance 
purposes by varying the horizontal alignment of the barrier 
can also provide visual relief. (See Figure 3-13.) In 
general for both visual and safety considerations, the access 
breaks in the wall should be designed to avoid an abrupt wall 
facing the flow of traffic. Where a solid door is not provided 
for access, the overlap of the parallel barrier walls should be a 
minimum of twice the width of the opening and be treated with 
absorptive material, in order to maintain the acoustical effec- 
tiveness of the wall. 

Another maintenance consideration with noise barriers is 
maintaining a stock of materials which are compatible with 
the barrier for replacement. This can be a serious problem, 
especially with naturally weathered finishes such as a pressure- 
treated wood. 



3-26 



FENCE 



WALL 




SPLIT AREA CREATES 
MAINTENANCE PROBLEMS 



LOW MAINTENANCE PLANTING 
SUCH AS STREET TREES 



WALL ALONG PROPERTY LINE 
ELIMINATES NEED FOR FENCE 




MAXIMUM DISTANCE FROM 
TRAVELED WAY 



FIGURE 3-12. 



MAINTENANCE CONSIDERATIONS CONCERNING 
LANDSCAPING 



3-27 




AVOID END WALLS EXPOSED 
TO FLOW OF TRAFFIC 




ACCESS DOOR 




DESIRABLE WALL SETBACK 

PLAN 



GURE 3-13. PROVIDING ACCESS FOR BARRIER MAINTENANCE 



3-28 



Finally, snow removal may affect maintenance in the case 
of earth berms used as noise barriers. In this situation 
care should be taken to see that the planting materials used 
on the earth berm are resistant to the effects of salt and 
other chemicals which may be encountered in snow removal areas 

3-5 Aesthetics 

A major consideration in the design of a noise barrier is 
the visual impact on the adjoining land use. Primary factors 
include scale relationship between the acoustic barrier and 
activities adjoining the highway right-of-way. Specifically, 
a high noise barrier adjoining a low-scale single family 
detached residential area could have a severe adverse visual 
effect. In addition, the high-scale wall placed close to 
residences creates adverse shadows and may affect the micro- 
climate. One solution to the problem of this scale relation- 
ship is to provide a stepped wall to reduce the visual impact 
through introduction of landscaping in the foreground; this 
allows additional sunlight and air movement in the residential 
area. In general, it is desirable for the wall to be located 
about four times its height from residences and landscaped to 
avoid being visually dominant (see Figure 3-14) . 

The visual character of noise barriers should be carefully 
considered in relationship to the environmental setting. 
In general, barrier concepts utilizing extensive landscaping 
are the most visually pleasing of any type of wall (see Figure 
3-15 and 3-16) . Walls should, as much as possible, and where 
desirable, reflect the character of their surroundings. Where 
strong significant architectural elements occur in close proxi- 
mity to wall locations, a relationship of material, texture, 



3-29 



Less than 1 . 5 H 




BARRIER BECOMES VISUALLY DOMINANT, 
POTENTIAL SHADOW PROBLEMS, £ 

VIEWS OBSCURED ^ 



' . ' . ' .' ' •"• ' .v i ' . ' .v.' t 



ram n on 



UNDESIRABLE BARRIER RELATIONSHIP 



2 to 4 H 




VISUAL DOMINANCE REDUCED - 
LANDSCAPING FURTHER REDUCES 
BARRIER IMPACT 



o i nm 'CD g 



ACCEPTABLE BARRIER RELATIONSHIP 



4' TO 6' WALL IN SCALE 
WITH BUILDING 




4 or more H 



BERM, LANDSCAPING 
SOFTEN BARRIER IMPACT 



n 



DESIRABLE BARRIER RELATIONSHIP 



FIGURE 3-14. 



SPATIAL RELATIONSHIP OF BARRIER TO 
ADJOINING LAND USE 



3-30 




UNDESIRABLE 




DESIRABLE 



FIGURE 3-15 



LANDSCAPING CAN BE VISUALLY PLEASING TO 
BOTH THE COMMUNITY AND THE DRIVER 



3-31 




PLAN 




• 




• 




FIGURE 3-16. 



USE OF LANDSCAPING TO IMPROVE BARRIER 
APPEARANCE 



3-32 



♦ 



and color should be explored, as shown in Figure 3-17. In 
other areas, particularly those closely related to freeway 
structures or other transportation elements , it becomes 
desirable that the barriers have a strong visual relationship, 
either physically or by design concept, to the highway elements 
See Figure 3-18 for an example. 

In general, a successful design approach to acoustical barrier 
walls is to utilize a consistant color and surface treatment 
with landscaping elements used to soften foreground views of 
the barrier. It is generally desirable to avoid excessive 
detail or a painted candystripe effect which tends to increase 
the visual dominance of the barrier (Figure 3-19) . 



Another important consideration is the impact of the noise 
barrier on the driver. At normal highway speeds, visual 
perception of noise barriers will tend to be of the overall 
form of the wall, its color, and texture. Due to the scale 
of acoustic barriers, the primary objective to achieve visually 
pleasing barriers will be to avoid a tunnel effect through 
major variations in form, wall type, and surface treatment. 
The most desirable visual treatment of noise barriers is 
generally through the use of landscaping material. 

The design approach to noise barriers will vary considerably 
depending upon highway design constraints. For example, the 
design problem both from an acoustic and visual standpoint 
is substantially different for a straight highway alignment 
with narrow right-of-way and little change in vertical grades, 
than for a highway configuration which changes horizontal and 
vertical alignments and has a large right-of-way. In the former 



3-33 



• 



Relate Materials 




t 



FIGURE 3-17. 



RELATING BARRIER DESIGN TO ARC H IT ECTUR AL 
ELEMENTS IN THE COMMUNITY 



3-34 



• 



► 



Barrier Wal 1 



Relate Materials 




FIGURE 3-18. 



RELATING BARRIER DESIGN TO OTHER 
HIGHWAY ELEMENTS 



I 



3-35 



t 



— 



i 



i 



— ' 




I 



I 



AVOID CONTRASTING 
PAINTED "CANDYSTRIPE" 
EFFECT 




USE SIMPLE TEXTURE AND 
LANDSCAPING TO SOFTEN 
WALL 



• 



FIGURE 3-19. VISUAL CONSIDERATIONS IN BARRIER DESIGN 



3-36 



♦ 



case, the highway designer is limited in the options of visual 
design to minor variations in form, surface treatment, and 
landscape treatment. With a generous right-of-way adjoining 
the traveled way, the highway designer has the opportunity 
to vary wall type, utilize landscaped berming, and other 
approaches to develop a visually pleasing acoustic barrier. 

One of the most positive approaches that the highway designer 
can take to improve the visual appearance of the barrier is 
by varying the forms and types of barrier wall along the length 
of the highway. Due to the high speeds traveled and associated 
perception, it is necessary for the highway designer to work 
with relatively major changes in visual form to significantly 
improve the appearance of the barrier. 

Alternative concepts for changes in the visual form of the 
barrier are illustrated in Figures 3-20 and 3-21. Some of 
the major options open to the highway designer include straight 
barrier wall, straight barrier wall with variation in depth, 
height and panels, and a barrier wall with curvilinear form. 

A second major concept in varying the form of barrier walls 
is with a diversity of wall type to give visual relief to 
the barrier. Basically this concept involves working with 
the barrier wall and landscaped earth berms to provide both 
continued acoustic attenuation and visual diversity along 
the length of the barrier (Figure 3-22) . 

From both a visual and safety standpoint, barrier walls should 
not begin or end abruptly. A gradual transition from the 
ground plane to desired height can be achieved several ways. 
One concept is to begin or terminate the wall in an earth 



3-37 



Wall 




CREATING A VARIETY OF SPACES 




LINKING DIFFERENT SIZE WALLS 



FIGURE 3-20. VARYING THE VISUAL FORM 



3-38 



• 



• 




BREAK WALL AT COLUMNS 



» 




PLANTER USED AS TRANSITION 
FROM LOW TO HIGH WALL 



. ,,,.■.,., ? 



MUM ■1,1 IiViIIImI 



PLAN 




FIGURE 3-21 . 



CONNECTING DIFFERENT HEIGHT WALLS TO 
VARY VISUAL FORM 



3-39 



> 




t 



PLAN 





: ---'--' ■■• *■ ■ •• B '' ' 



ELEVATION 



FIGURE 3-22. USE OF BERM TO CONNECT WALLS AND ADD 

VARIETY 



3-4 



♦ 



berm mound. Other concepts include bending back and sloping 
the wall, curving the wall back in a transition form, stepping 
the wall down in height, and terminating in a wall planter. 
The concept of terminating the wall with a planter should be 
utilized only in areas where the edges will be protected from 
potential conflict with highway traffic. These approaches are 
illustrated in Figures 3-23, 3-24, and 3-25. 



3-6 Materials and Designs 

A variety of materials may be used for noise barriers. The 
approach taken in this handbook is to provide detailed en- 
gineering designs, called "reference drawings," for several 
materials which have been used as noise barriers with good 
results: concrete, masonry, steel and wood for barrier walls, 
and earth berms. These drawings may be found in Appendix A. 
Each of the basic materials under consideration is first 
presented in reference drawing format with subsequent modifi- 
cations for various alternative surface treatments for visual 
and weathering purposes. Appendix B provides similar drawings 
for steel and wood walls designed specifically for use on 
elevated structures. Finally, reference drawings are provided 
in Appendix C for sound absorbing treatments which may be applied 
to barrier walls. 

Due to the extreme variations and conditions encountered 
throughout the country, it is not possible to prepare a 
standardized wall construction detail which is applicable 
in every locality and for the entire scope of any individual 



3-41 




UNDESIRABLE 



• 




• 



WALL ENDS IN MOUND 



FIGURE 3-23. USE OF EARTH MOUND TO TERMINATE WALL 



3-42 



• 



.r- r ' 











BEND BACK AND SLOPE 
(ABRUPT WALL ENDS CAN BE 
CONCEALED WITH PLANTS) 




CURVE TOWARD GROUND 




STEP DOWN IN HEIGHT 



FIGURE 3-24. 



ALTERNATE MEANS OF TERMINATING BARRIER 
WALLS 



3-43 



Planters 




z 



Wall 



PLAN 




FIGURE 3-25. 



USE OF PLANTER TO TERMINATE WALL 
(in protected areas only) 



3-44 



• 



project. However, generalized criteria have been utilized 
in the design of all barriers which may be applicable to a 
great number of highway design projects. As indicated on 
the reference drawings, each wall system has been designed 
for heights of five, ten, fifteen, and twenty feet. In 
addition, appropriate wall designs are provided for wind 
loadings of twenty, thirty, and forty pounds per square foot. 
It must be understood by the highway designer that each pro- 
ject will need to be designed for the specific wind, soils, 
and other conditions encountered for that project unless 
the conditions conform to those outlined in the design 
criteria indicated on the specific reference drawings. 

In addition, the AASHTO guide "Standard Specifications for 
Structural Supports for Highway Signs, Lumminaries and Traffic 
Signals" (Reference 3-4) should be considered by the designer 
and used as appropriate. 

In general, the wall systems have been designed to span 
horizontally between columns with pier support foundations. 
The rationale for this design approach is to allow the 
highway designer the greatest flexibility in wall placement 
and location and to avoid problems of varying horizontal 
and vertical alignments of the highway. The basic wall type 
reference drawing incorporates the following information: the 
height of the wall; the spacing between columns; the depth of 
the foundation pier support; the diameter of the foundation 
piers; the size of the column supports; and the size of the 
thickness of the material of the basic wall structure. This 
information is presented for the three typical wind loading 
conditions. 



3-45 



The structural design criteria have excluded consideration 
of vehicle impact since in many situations, the barrier 
wall will be located either behind crash barriers or suffi- 
ciently far from the traveled way to eliminate the need for 
crash barrier protection. If the local project, due to 
limited right-of-way, requires the placement of the acoustic 
barrier closer than thirty feet from the edge of the traveled 
way, the highway designer may wish to either provide a separate 
guard rail or crash barrier or, alternatively, utilize the 
potential crash situation as the design criteria for structural 
design of the acoustic barrier. Snow loads are a localized 
condition and should be considered by the highway designer. 
Consideration should also be given to providing drainage under 
the barrier. 



3-6.1 Concrete Barriers 

The basic wall configuration developed for concrete barriers 
is a system of four inch thick precast concrete panels, spann- 
ing horizontally between poured-in-place concrete piers supported 
on pier foundations. The basic wall system has been developed 
as a precast approach due to economic considerations and versa- 
tility with respect to varying conditions likely to be encountered 
by the highway designer. Typically, the precast panels span 
between poured-in-place columns varying between ten inches square 
to fifteen inches square, depending upon the height of the wall 
and the local wind pressures. 

An alternative modification of the basic precast concrete 
wall is to utilize the precast panels spanning between 
steel columns which are, in turn, set in piers instead of 
utilizing poured-in-place concrete columns. The advantage 
of this approach is to minimize the on-site fabrication and 
forming work required to erect the wall. 

3-46 



• 



t 



• 



Surface treatments for concrete walls offer the highway- 
designer many opportunities for good visual design at a 
nominal cost. Several are illustrated in Appendix A in 
Figure C-3. The various surface treatments for concrete 
walls include forming the concrete with random width boards, 
form inserts, utilizing a fine line ribbed texture formed by 
inserting a rubber mat prior to pouring the concrete, 
and reinforcing bars inserted in the forms for a rough tex- 
tured surface finish. Another method of achieving a surface 
texture is through use of "Bomanite" which is a franchised 
method of press forming concrete slabs. Several patterns 
are available using this system. Alternative surface approaches 
would include use of an exposed aggregate surface finish or 
sandblasting the concrete wall. Due to maintenance considera- 
tions, it is generally not desirable to paint the concrete 
surface. However, if a colored surface is desired, this can 
be achieved either through an integral color additive mixed 
with the concrete or through the careful selection of aggregate 
and cement-type mixes to present a finished wall surface which 
is visually pleasing. 

Additional surface treatment of concrete walls can be accom- 
plished by the highway designer through the surface application 
of other materials. One example would be the application of 
pressed wood fiber panels applied to either a new or existing 
concrete wall to act as an acoustical absorbing material. 
Other materials which could be applied to a concrete wall 
include brick veneer, stucco, and similar materials. 



3-47 



Variation in the horizontal alignment of the concrete barrier 
wall is desirable both from a visual and functional considera- 
tion. One method of offsetting bays of the concrete panels 
is to place the panel either front-face or rear-face of the 
concrete piers. 

3-6.2 Concrete Masonry Unit Walls 

The basic wall configuration for concrete masonry units is 
based on a six-inch wide by sixteen inches long standard 
block module. The wall is supported on pier foundations. 
At each foundation pier, vertical reinforcing steel extends 
through the hollow cavity of the pier which is then grouted 
solid to form a column from which the concrete masonry units 
span horizontally. 

A basic concrete masonry unit wall with no surface treatment 
is generally unacceptable from a visual standpoint. Alter- 
natives to the standard concrete masonry unit wall include 
utilizing special blocks with scored, combed, or other surface 
characteristics. Some of the commonly available block designs 
including slumpstone are illustrated on Figures M-3 and M-4 
in Appendix A. 

In addition to alternative surface treatment from the standard 
concrete masonry unit wall, the highway designer may also con- 
sider alternative methods of laying up the masonry wall such 
as stack bond. Various wall patterns as illustrated in Figure 
3-26 include common bond, stack bond, and the use of a four 
inch module. It should be recognized by the highway designer 
that while special surface blocks normally involve an addi- 
tional cost, with the scale of many highway projects special 
blocks could be utilized at nominal additional costs. 



3-48 



• 



t 



• 



— «»"i»a I 



COMMON BOND CONCRETE 
BLOCK WALL TENDS TO BE 
MONOTONOUS 



















































































































































: 







































FIVESCORE BLOCK UNIT WITH 
INTEGRAL COLOR PROVIDES 
PLEASING TEXTURE 



l .i. ■■■ A — y ■ t »... — —It — i | . I . ■■■ « M l*ii i 

■ ;; ■*■ . i. ■-■ . * ■■ -)| ■■;-)- i i- ■-'•II I'll' 



4" SLUMPSTONE MODULE IN 
SCALE WITH RESIDENTIAL AREA 



FIGURE 3-26. ALTERNATE BLOCK WALL PATTERNS 



3-49 



\nother alternative concrete masonry unit wall is constructed 
in prefabricated panels. In this type, automated block-laying 
machines can form panels up to twelve feet high and twenty 
feet long with standard blocks. This type of wall is normally 
constructed between piers and it is possible to use colored, 
split-face, single- or multi-score blocks. 

3-6.3 Steel Barriers 

Steel acoustical barriers are of two basic types. The first 
type is constructed of steel decking spanning horizontally 
between steel columns and the second type is made with steel 
sheet piling which acts as both the wall and the foundation 
support for the wall. 

The basic steel decking wall consists of a ribbed steel deck 
spot welded to steel columns, as illustrated on Figure S-l. The 
basic steel deck wall can be modified by adding sheet metal 
closure strips covering the spot weld joints and a cap rail if 
so desired by the highway designer. An alternative approach 
to the basic wall configuration is to construct channel sec- 
tions on top and bottom spanning between columns; then the 
sheet metal decking would span vertically between the channel 
sections . 

The barrier wall constructed of sheet steel piling offers the 
highway designer considerable flexibility in vertical and 
horizontal alignment in that the individual sections of sheet 
piling act as their own foundations for the wall. The verti- 
cal lines of the sheet piling can be visually attractive. 



3-50 



t 



• 



• 



Surface finishes for the steel barriers can be weathering 
steel such as "Corten" which is allowed to oxidize and 
requires no further maintenance. Care should be taken in 
utilizing weathering steel in relationship to concrete, in 
that during the initial oxidation period, it can leave streaks. 
Alternatively, both the sheet metal decking and the sheet piling 
can be painted. 



3-6.4 Wood Barriers 

The basic wood barrier indicated on the reference drawings 
uses two inch thick tongue-in-groove decking to span 
horizontally between wood posts which in turn are anchored 
to concrete pier foundations. The use of wood can be a 
visually pleasing warm material alongside the highway. 

Specific surface treatments to improve the visual appearance 
of the wood wall include placing a top rail and random-spaced 
vertical battens along the length of the wall. Another concept 
is to utilize rough-sawn and textured plywood patterns as shown 
on Figure W-2. 

There are several alternative methods of treating the wood 
walls to protect them from exposure to the elements includ- 
ing utilizing wood preservative, staining, and letting the 
wood age naturally. Letting the wood age naturally is only 
suggested for wood such as redwood and cedar which will accept 
this kind of exposure. Due to long-term maintenance considera- 
tions, painting of the wood wall is not suggested. 



3-51 



3-6.5 Earth Berms 

Planted earth berms are usually superior to barrier walls 
from aesthetic considerations and may be more economical 
if fill material and right-of-way are available. Slopes 
of 4:1 or flatter are best from a visual point of view but 
2:1 slopes are acceptable if the circumstances warrant. 

The main disadvantage of berming is that large areas of 
right-of-way are required for mounds of significant height. 
Combining walls and berms allows for more height in a limited 
right-of-way and more flexibility in the location of walls 
(see Figures 3-27 and 3-28) . In situations where right-of- 
way width does not permit adequate mounding to occur, a 
wall built on top of a mound extends its height. In most 
cases this would cost less than a wall of equal height and 
increases the aesthetic possiblities . Berms can also serve 
as connecting points for walls or walls of different heights 
adding variety to possible severe directional design. 

It should be noted however that there is at present serious 
concern in the scientific community that extensive landscap- 
ing along the top of a berm can degrade its attenuation 
characteristics by scattering the diffracted sound energy. 
This phenomenon merits further investigation. For the 
present it is recommended that landscaping along the top of 
berms be kept to a minimum. 



3-52 



• 



• 



♦ 



R/W from Edge of Shoulder 




Rounding Top Edge Desirable 



Existing Grade 



TYPICAL BERM CONFIGURATION 




^Edge of Shou 



Ider 



*Dictated by Safety 
Considerations 



BERM IN LIMITED RIGHT-OF-WAY 



FIGURE 3-27. 



ALTERNATE APPROACHES TO BERM 
CONSTRUCTION 



3-53 



♦ 




FIGURE 3-28. WALL AND BERM COMBINED TO CREATE 

MORE HEIGHT IN LIMITED RIGHT-OF-WAY 



# 



3-55 



♦ 



3-6 . 6 Noise Barriers * ny, _ Elevated Str uctures 

The two basic barrier; ..suable for use on elevated structures 
are wood barriers and steel barriers. Due to weight considera- 
tions, concrete and concrete: masonry are not suitable. The 
conditions of use encountered ^ 2 the highway designer for 

noise barriers on elevated st itures include bridges, ramps, 

and elevated roadway grade separations. 

It is quite possible that rr.r.vy of these noise barriers will 
be implemented on existing structures in which there are 
several factors to be taken into account by the highway 
designer. One factor is shy distance: there should be a 
minimum of four feet from the 2dge of the traveled way to 
the barrier for adequate shy distance , The second major 
factor to be considered on existing structures is the 
structural design of the existi^'j bridge or ramp. If in the 
original design v ^ horizontal loading forces calculated 
for the guardrail are equal to or greater than the forces 
generated by placing the noise barrier and associated wind 
loads, then the existing structure may be suitable for 
installation of the barrier. In addition, it will be necessary 
to evaluate the existing structure to determine if sufficient 
surface area along its edge is available to adequately anchor 
the barrier. 



3-6.7, Absorption Treatments for Noise Barriers 

There are four basic materials which have been considered for 
absorption treatments to be used with noise barriers. These 
absorption treatments are resonant cavity concrete masonry 
units, glass fiber batts, wood fiber planks, and spray-on 
treatments such as vermiculite :r oeriite aggregate concrete. 



3-55 



Resonant cavity concrete masonry units are suitable for both 
free-standing acoustic barrier walls and for an absorptive 
treatment in locations such as tunnels and underpasses. The 
concrete masonry units are a standard concrete masonry block 
with slotted apertures to allow a resonance inside the block. 
This type of block is a proprietary product called "Soundblox, " 
as manufactured by the Proudfoot Company. 

Glass fiber batts are a suitable material for use on free- 
standing acoustic barriers, tunnels, and underpasses. The 
glass fiber batts are two inches nominal thickness, one and 
a half pound cubic foot density and wrapped in a protective 
covering of 1.5 mil thickness mylar. The batts then are 
stapled to wood runners which allow a minimum two inches air 
space behind the glass fiber batts. The front face of the 
glass fiber batts is protected by the use of random wood 
battens which leave a minimum surface area opening of 50%, 
or alternatively by perforated metal panels which have an 
open area equal to a minimum of 30 to 40% of the surface 
area. 

The third type of acoustic absorption material is pressed 
wood fiber boards. To be suitable for use in an exterior 
location this material should be manufactured with a suitable 
binder and protected from deterioration weathering by the 
use of exterior non-bridging type latex paint. The pressed 
wood boards should also be treated with f ire-retardant chemicals 
in the manufacturing process. These boards may be nailed or 
attached directly to the supporting structural system, allow- 
ing a six to sixteen inch air space behind the board for 
optimum performance. In addition, the wood fiber boards should 



3-56 



• 



♦ 



♦ 



be located where they are not subject to road splash. It 
must be emphasized that, while several wood fiber planks 
are available, the feasibility for exposure to weathering 
and cleaning must be verified for the specific product 
under consideration. 

The fourth type of acoustical absorption material is a 
spray-on system of Portland cement concrete with a light- 
weight perlite or vermiculite aggregate. This product may 
be sprayed onto a high rib metal lath which in turn main- 
tains a two-inch air space behind the material. Due to the 
possibility of this material spalling in freezing temperature, 
it is not recommended for use where exposed to saturation, 
then freezing. This material should also be protected by 
the use of a non-bridging exterior latex paint or silicone 
treatment. 



3-6.8 Other Materials 

The materials for which reference drawings have been prepared 
are by no means the only materials which can be used for noise 
barriers. Information about various other materials is also 
provided in Chapter 4 . 

In the design of barriers using these materials, the highway 
designer may use the reference drawings to provide guidance. 
Care should be taken to minimize the possibility of openings 
in the barriers. 

Reference 1-4 provides a catalogue of sound absorbing 
materials which may be used along highways. Additional 
sound absorbing treatments may be selected from that 
report. The report also provides further details of the 
weathering properties of the various materials. 

3-57 



3-7 Costs 

A "cost factor" in dollars per lineal foot has been developed 
for each wall design on each reference drawing. These cost 
factors include the cost of barrier construction, but not 
the cost of any right-of-way acquisition or easement purchase. 
Also, no attempt has been made to quantify cue tuai.s of main- 
tenance of a particular barrier. 

The primary use of the cost factors is to compare the relative 
costs of several barrier design options. ^ince the cost of 
barrier construction is one of the major considerations in 
the decision-making process, a rank ordering of alternate 
design options by cost factor may be very useful in selecting 
an optimum barrier design. 

The cost factors may also be used to estimate total barrier 
costs for preliminary planning purposes (but the assumptions 
used to develop the cost factors should be clearly understood, 
as discussed below) . When a final design has been selected 
and refined, an accurate cost estimate should be prepared 
by the designer. 

For materials not included in the reference drawings, cost 
factors (on a square foot basis) are also provided. While 
the cost factors for the reference drawings were determined 
by evaluation of all the construction details, the cost factors 
for the other materials were approximated and may not include 
the costs of structural members for some designs. Thus, care 
should be taken in using these approximate cost factors, par- 
ticularly for estimating total barrier costs. 



I 



t 



3-51 



« 



The cost factors indicated on the reference drawings are 
based on a cost factor of 1.00 = $1.00 per lineal foot of 
barrier wall in 1975 dollars. To provide this cost estimate, 
several assumptions have been necessary: costs are based 
on San Francisco Bay Region prices; the project size is 
3,000 lineal feet; and there has been no allowance for 
traffic detouring. The material necessary for construction 
of the earth berm is considered to be imported from a distance 
of five miles. 

In order for the cost factor estimates to be properly 
utilized, the highway designer will have to adjust for 
the particular geographical location in accordance with 
the data provided in Chapter 4 relating relative costs in 
105 cities around the country. In addition, costs should 
be escalated from 1975 dollars to the time of construction. 

As an indication of the costs of the basic barrier designs 
provided in the reference drawings, Figure 3-29 shows the 
cost factors for the various designs as a function of height 
(using a wind loading of 30" pounds per square foot as an example) 
Figure 3-30 illustrates the increased costs (based on a 15 
foot high barrier) when various aesthetic and/or weathering 
treatments are applied. These treatments are detailed in 
Appendix A. Note that fairly simple and inexpensive treat- 
ments (such as painting or staining) have not been included 
on the figure. 



3-59 



300 



c 
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200 



100 



BASIC BARRIER 
30 %h Horizontal Loading 




.• Steel 



• Concrete 

• Wood 



• Masonry 

• Berm 



« 



♦ 



10 15 

Barrier Height, Ft 



20 



FIGURE 3-29 Construction Costs for Various Barriers 



3-60 



♦ 



200 



175 



150 



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15 Foot Barrier 
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X Basic Barrier 

X-Y Weathering/Aesthetic 
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see Appendix A 
for description. 



• M-2 



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/ 



M-3.M-5 



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• M 



Steel 



Wood 



Masonry Concrete 



Berm 



FIGURE 3-30 



Construction Costs for Barriers with Additional 
Treatments . 



3-61 



3-8 Community Participation in the Barrier Design Process 

Highway noise exposure in community areas adjoining major 
facilities can cause annoyance, interference with speech 
and sleep, and disruption of work and recreational activities. 
It can create feelings of dissatisfaction with the community, 
and aggrevate a resident's attitudes toward the highway. While 
construction of a noise barrier which reduces this exposure 
may provide significant relief, a barrier which is poorly 
designed from the point of view of aesthetics, or which creates 
unpleasant visual impacts because of out-of-scale proportions 
can further aggrevate the community and in some instances add 
to the feeling of isolation that may have been created when 
the facility was first constructed. 

By permiting active community participation in the development 
of barrier plans, beyond the minimum requirements for public 
hearings, there is greater likelihood that the barrier would 
be accepted and appreciated. As indicated in Figure 3-1, 
this involvement should be incorporated throughout the design 
process. 

Public involvement should begin early, in the stage where 
various noise abatement options are being explored. For 
a particular community, use of a barrier wall may not be 
desirable; this type of information is only obtained through 
knowledge of community attitudes and preferances. 



3-62 



♦ 



« 



Once the desirability of a noise barrier has been established, 
consideration of community additudes and desires will help 
set design criteria. If it is known that the community views 
its noise exposure as being severe, then reducing that exposure 
by a few decibels to meet specific noise standards (although 
complying with appropriate regulations) will do little to 
solve the community's problem and will only result in a waste 
of funds and a loss of credibility. 

Selection of barrier location, materials, and ultimate 
design can benefit from community involvement and review. 
Not only will a better understanding of community preferances 
be gained by the highway designer, but an understanding of the 
available options as well as constraints facing the designer 
will be gained by the community. This mutual understanding of 
community needs and attitudes and highway design constraints 
and limitations will greatly enhance the barrier design process, 



3-63 



♦ 



( 



« 



CHAPTER 4 
BARRIER DESIGN PROCEDURE 

When faced with the problem of designing a noise barrier to 
reduce roadway traffic noise to within certain desirable 
levels, various questions come to mind: 

• Where should the barrier be placed? 

• How high? 

• How long? 

• What materials should be used? 

• Should it be a wall or berm? 

In addition to these questions concerned with the physical 
characteristics of the barrier, questions concerning the 
economics and functional performance of the barrier must be 
answered as well: 

• How costly will the barrier be? 

• Will it be accepted by the community as 
well as the highway user? 

• Will it create safety problems? 

• Will there be any maintenance or durability 
problems? 

Before these questions can be answered, it should be recog- 
nized that if it is possible to build a barrier which will 
provide the required noise reduction, then generally there 
are many such barriers which will provide the necessary 
reduction. One approach to the design of a noise barrier, 



4-1 



and indeed the approach to be taken in this chapter, is to 
define all reasonable barriers (or, at least, many such 
barriers) which will fulfill the required noise reduction, 
and provide sufficient information about each barrier to 
permit a rational selection of the barrier most appropriate 
for a particular set of local conditions. 

This chapter details a barrier design procedure incorporating 
the following major steps: 



Step 1 
Step 2 
Step 3 
Step 4 
Step 5 
Step 6 
Step 7 
Step 8 
Step 9 



Determine Noise Reduction Design Goals 
Define Site Characteristics 
Determine Geometrical Alternatives 
Identify Additional Barrier Treatments 
Select Design Options 
Define Cost Factors 
Assess Functional Characteristics 
Select Barrier 
Design Barrier 



♦ 



These steps form the framework for specification of barrier 
requirements, determination of barrier options which would 
satisfy these requirements, and selection of an optimum 
design based on assessment of acoustic and functional charac- 
teristics and cost. 

This procedure is intended to be used in conjunction with 
other tools available to the highway designer according to 
the following scenario: 



4-2 



« 



Stage I. A current or anticipated highway- 
noise problem is identified. 
Noise levels are determined using 
the 117/144 or TSC methodology 
(or through field measurements) , 
and possibly noise contours are 
prepared. Noise criteria are es- 
tablished and critical receivers 
are identified. 



Stage II. Among the options considered to 
reduce noise exposure is the use 
of noise barriers. Using the 
design procedure in this chapter 
the approximate physical dimensions 
of alternate barriers are determined, 
several design options are developed 
and evaluated, and a single design 
is selected based on its acoustical 
and non-acoustical characteristics 
and cost. 



Stage III. The physical dimensions of the barrier 
design are refined and optimized, and 
a final design is prepared. This pro- 
cess is facilitated by use of the TSC 
computer program. 

The procedures of this chapter specifically address Stage II 
activities. There are several important points about all three 
stages that should be emphasized, however. First, in order to 
begin the procedure that follows the designer must have pre- 
viously determined "before" noise levels at critical receiver 
locations. Second, for the purpose of easily defining possible 
barrier dimensions so that various design options can be developed, 
the procedure entails a simplified assessment of barrier attenu- 
ation, which provides only gross (but conservative) dimensions 
in terms of necessary height and length. Use of these approxi- 
mate barrier dimensions is certainly adequate, however, for 



4-3 



evaluating and selecting the design options. Finally, only 
by use of a computer can the myriad highway, traffic and 
community parameters influencing noise exposure be properly 
accounted for. Once a design is chosen, the TSC computer 
program should be used to help optimize barrier dimensions, 
which should result in a less costly design. 

In using the procedure in this chapter, the designer should 
be guided by the considerations discussed in Chapter 3. 
Examples of the calculations and of the use of nomographs, 
charts, etc., are included throughout this chapter; complete 
examples of the procedure are provided in Chapter 5. 

4-1 Step T. Determine Noise Reduction Design Goals 

In this step the desired noise reduction characteristics of 
the barrier are defined, and their feasibility is evaluated. 

1.1 Prepare a route map to a convenient scale. Identify 
critical receivers along the route where there is a noise 
impact based on projected or measured noise levels. Select 
at least six such receiver locations: the closest to the 
roadway and the farthest from the roadway at both ends of 
the community and somewhere in the middle of the community 
(see Figure 3-8) . 

1 . 2 Draw a perpendicular from one critical receiver to the 
roadway center line (if the roadway curves about the receiver 
so that there is more than one such perpendicular, choose the 
shortest perpendicular) . 



4-4 



* 



♦ 



1.3 Measure the near-lane distance D N (distance to the center 
of the near-lane) , and the far-lane distance D F (distance to 
the center of the far-lane) . Calculate the equivalent lane 
distance D E as follows: 



D E = V D N X D F <4 " 1) 



Example. A receiver is located 125 feet from the edge of 
the near lane of a highway with eight 12-foot 
lanes and a 30-foot median. The distance to 
the near lane D^ is 125 + 6 = 131 feet, and to 
the far lane D F is 125 + (7 x 12) + 6 + 30 = 
245 feet. See Figure 4-1, The equivalent lane 
distance is thus 

Nl31 x 245 = 179 feet. 



1.4 Refer to the Design Goal Worksheet, Figure 4-2. Enter 
the equivalent lane distance D E on Line 1. 

1.5 Enter on Line 2 the "before" barrier noise level, L B , 
in dBA. (Either L^q or L e _ may be used.) 

1.6 Enter on Line 3 the desired criterion level Lp, in 

dBA (in terms of L-. Q or L , whichever was used in Step 

1.5) . 

I 

1.7 The desired insertion loss is given by L B - Lq. Enter 
on Line 4 . 

1.8 On Line 5 enter the method by which L B was determined. 
Was it 117/144, TSC, or field measurements? 



4-5 



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4-6 



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4-7 



1.9 If L B includes the effects of shielding between the 
source and receiver, determine the magnitude of the shielding 
attenuation A g (excluding the shielding from houses and vege- 
tation) . If the prediction procedure used to determine L B 
does not readily indicate A s , it may be determined by predict- 
ing L_ with and without the shielding element present. (If 
field measurements were used, refer to the Barrier Nomograph 
[Figure 4-13] to estimate the attenuation provided by the 
shielding element.) Enter A on Line 6. 

1.10 If the TSC method was used to determine L B , A G is zero. 
If 117/144 was used, Figure 4-3 indicates A G as a function of 
the equivalent lane distance D E . Enter Aq on Line 7. 

Example. Assume the 117/144 method was used to determine 
Lb- For DE = 179 feet, A G is 2.5 dBA. For 
D E = 500 feet and beyond, A G is 5 dBA. 

1.11 If L B was measured at several representative locations 

in the field, the propagation loss factor for the actual terrain 
can be determined. If this is closer to 3 dB than to 4.5 dB 
per doubling of distance, Aq = 0. If it is closer to 4.5 dB 
than to 3 dB, use Figure 4-3 to find Aq. Enter on Line 7. 

1.12 Determine the Design Goal noise reduction by adding 
Line 4 to the larger of Lines 6 and 7. Enter on Line 8. 

(This is the total reduction required to achieve the desired 
criterion level, not the additional reduction beyond that 
presently available.) 

1.13 If the desired reduction is 20 dB or greater (Line 9), 

it is not feasible to obtain using a noise barrier. Additional 
methods of noise control should be considered. 



♦ 



4-8 



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100 



200 



400 



800 



Equivalent Lane Distance Dr, ft, 



FIGURE 4-3 Ground Effect Attenuation. 



4-9 



1.14 Steps 1.2 through 1.13 should be performed for each 
critical receiver from the roadway. 

4-2 Step 2: Define Site Characteristics 

As input to the process of selecting appropriate locations 
for noise barriers, it is useful to identify those areas along 
the roadway where barriers cannot be constructed, and to point 
out the factors that provide constraints on the location or 
structural requirements of the barrier. 

2.1 Delineate the existing right-of-way on the route map 
prepared in Step 1. 

2.2 Delineate those areas beyond the right-of-way which 
might be acquired through purchase or easements to provide 
additional locations for noise barriers if necessary. 

2.3 Identify those areas where a noise barrier should not 
be constructed because of safety factors, based on the 
following considerations. 

2.3.1 For curved on- and off-ramps, refer to Figure 4-4 
to determine the minimum setback distance m, as a function 
of the design speed and radius of curvature of the ramp. 



Example. See Figure 4-5 for an example of safety con- 
siderations for an on- or off-ramp. 



2.3.2 For intersecting ramps, refer to Figure 4-6. Deter- 
mine the sight distance d along the highway as a function of 
the design speed. For this setback distance, draw the sight 
line from the center of the near lane to the eye of the driver 
on the ramp. A noise barrier should not be located within 
the area defined by this sight line and the highway. 



4-10 



« 



* 



» 



Sight distance measured 
along this 




— y, object 



». ' .. ■ .> ■ . < . *> . • • ' .» . ■ . ■ .> • . ■ . » . ■ .■ ■ . »■ . 



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shoulder 



Acoustical 
vertical wall 
berm 



> 




5 10 15 20 25 

m= MIDDLE ORDINATE: 
CENTERLINE INSIDE LANE TO SIGHT 08STRUCTI0N-FEET 

MINIMUM STOPPING SIGHT DISTANCE 



35 



10 15 20 25 

m« MIDDLE ORDINATE: 

CENTERLINE INSIDE LANE TO SIGHT OBSTRUCTION-FEET 

DESIRABLE STOPPING SIGHT DISTANCE 



(Source: Reference 4-1) 



FIGURE 4-4 Safety Factors for On and Off Ramps, 



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4-11 





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4-13 



Example. See Figure 4-7 for an example of safety con- 
siderations for an intersecting ramp. 

2.3.3 For intersecting roadways, refer to Figure 4-8. Draw 
a line from the design speed on the major road (Axis A) to 
the design speed on the minor street (Axis B) . Select any 
two sets of coordinates D^, D2 along this line and plot on 
the route map. A straight line through these two locations 
will be the sight line; a noise barrier should not be located 
within the area between this sight line and the roadways. 

Example. See Figure 4-9 for an example of safety con- 
siderations for intersecting roadways. 

2.3.4 For bridges and other elevated structures, barriers 
should be located a minimum of four feet from the edge of 
the traveled way. 

2.4 Examine the area for topographic and neighborhood 
features which would limit barrier placement or necessi- 
tate barrier termination, such as traffic or pedestrian 
bridges over the roadway, immediately abutting residential 
dwellings, etc., and note these on the route map. 

2.5 Determine wind load requirements and soil characteristics 
for later use in designing barriers. If appropriate, determine 
requirements imposed by snow loading. 

2.6 If the noise barrier is to be constructed on an existing 
elevated structure, the structural design of this element 
should be re-evaluated to determine the suitability for con- 
struction of a barrier. 



• 



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4-14 



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Then d = 660 feet 

Barrier cannot be placed in 
shaded region. 



FIGURE 4-7 Example of Safety Considerations for 
Ramp Intersections. 



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4-15 



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4-16 



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4-17 



4-3 Step 3: Determine Geometrical Alternatives 

This step provides a methodology for "designing" the noise 
barrier to achieve the desired reduction goals. In the m 

context of this step, the term "design" refers to determi- 
nation of the three basic physical dimensions of the barrier 
which affect its attenuation: its height, its length, and 
its location or setback relative to the roadway. Several 
alternative geometrical designs are determined in this 
step. 

At this point it is assumed that the transmission loss of 
the barrier will be sufficiently high so that the transmitted 
energy will be insignificant. It is also assumed that there 
are no multiple reflections from walls across the roadway to 
compromise barrier performance. Under these circumstances 
the barrier should be designed for an attenuation equal to 
the Design Goal noise reduction. If the designer can en- 
vision the use of materials with marginal TL properties or 
a multiple reflection situation, the barrier should be designed 
in this step for an attenuation higher than the Design Goal 
noise reduction. 

3.1 A nomograph will be used to evaluate barrier attenuation. 
Use of the nomograph requires knowledge of the following parame- 
ters: the line-of-sight distance between the source and the 
receiver; the break in line-of-sight by the top of the barrier; 
the barrier position relative to the source and receiver; and 
the angle subtended by the barrier as seen from the receiver. 
These parameters are illustrated in Figure 4-10, and defined in 
Figure 4-11. 



4-18 



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♦ 




ROADWAY 



BARRIER 



ANGLE SUBTENDED 



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FIGURE 4-10 Illustration of Barrier Parameters 



4-19 



Parameter 
Line-of-sight, L/S 



FIGURE 4-11 
DEFINITION OF BARRIER PARAMETERS 

Definition 



Straight line from the receiver to the source 
of noise. For roadway sources, this L/S is 
drawn perpendicular to the roadway. At the 
source end, the L/S must terminate at the 
proper source height: feet for automobiles 
and medium trucks, 8 feet for heavy trucks.* 
At the receiver end, the L/S must terminate 
at ear height (i.e., 5, 15, 25,...) feet 
above the ground depending upon the observer 
location. The L/S distance is the slant- 
length of the L/S, not the horizontal distance 
only. 



• 



Break in the L/S, B 



The perpendicular distance from the top of the 
barrier to the L/S. If the L/S slants, then 
this break distance will slant also. This is 
not the height of the barrier above the terrain, 



Barrier position, P 



Angle subtended, a 



Distance from the perpendicular break point in 
the L/S to the closer end of the L/S. This is 
also a slant distance.* 

Measured at the receiver in the horizontal plane ; 

the angle subtended by the ends of the barrier. 

For a barrier always parallel to the roadway, an 

infinite barrier would subtend 180°. 

barriers, the angle may also be 180° 

following cases: (1) if the barrier 

away from the roadway, so that the 

subtended is 180° or more, and (2) 

server cannot see the roadway past the ends of 

the barrier, due perhaps to terrain. 



For finite 
in the 
ends bend 
actual angle 
if the ob- 



♦ 



*Note that although the "L/S distance" and "barrier position distance" 
vary slightly for high and low sources, in practice either one may be 
used. However, the "break in the L/S distance" must be measured ac- 
curately for high (heavy truck) and low (automobiles and medium trucks) 
sources separately. 



4-20 



An overview of the Barrier Nomograph is shown in Figure 4-12. 
The wavey line in the figure is a representation of the 
barrier intruding above the line-of -sight, represented by the 
horizontal line on the bottom of the figure. The barrier can 
be moved horizontally back and forth, depending upon the 
barrier position; this horizontal movement is governed by the 
barrier position scale on the bottom of the figure. The 
barrier can move up or down, depending upon the barrier break 
in line-of-sight; the height of the barrier is determined us- 
ing the barrier break scale on the left of the figure. The 
top of the barrier falls on a curve of constant attenuation; 
this attenuation is translated to a numerical value depending 
upon the angle subtended, using the chart on the right of the 
figure. 

The line-of-sight length is used three times in the nomograph 
to normalize all distances to the scale of the drawing. The 
Barrier Nomograph, Figure 4-13, is used to determine the at- 
tenuation of a barrier for which L/S, B, P, and a are known 
as follows: 

3.1.1 Starting at the bottom, draw a line from the L/S scale 
through the Barrier Position scale to Turn A, and project 
vertically upwards. This line sets the position of the barrier 
relative to the source and the receiver. 

3.1.2 Starting at the left, draw a line from the L/S scale 
through the Barrier Break in L/S to Turn B, and project 
horizontally to the right. Where the two lines meet represents 
the top of the barrier. 



4-21 



L/S 



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ANGLE 
SUBTENDED 



BARRIER POSITION 



L/S 



♦ 



FIGURE 4-12 Overview of Barrier Nomograph. 



4-22 



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4-23 



3.1.3 Follow the attenuation curve on which the top of the 
barrier lies upward and to the right to Turn C, and then 

connect with the L/S scale in the center of the nomograph. m 

3.1.4 At the intersection of this line with the Pivot line 
project a line horizontally to the right until it intersects 
with the curve corresponding to the proper Angle Subtended. 

3.1.5 At the intersection with the Angle Subtended curve, 
project upwards to the Barrier Attenuation scale. 

Example. Figure 4-14 shows a section and plan view of a 
receiver near a roadway with car and truck 
traffic; the receiver has a line-of-sight dis- 
tance of 200 feet to the traffic sources. A 
barrier is also shown at a position 75 feet 
from the traffic stream, which provides breaks 
in line-of-sight of 3 and 8 feet, respectively, 
for the truck and car sources. Use of the 
Barrier Nomograph to determine the attenuation 
provided by this barrier is illustrated in 
Figure 4-15. For a subtended angle of 170 
degrees, the barrier provides 7 dBA attenua- 
tion for trucks, and 9h dBA attenuation for 
cars. 

With some familiarity, use of the barrier nomograph becomes 
relatively simple and straightforward. Note that the barrier 
nomograph can be used "backwards" — for a known attenuation, 
L/S and P, tradeoffs of B versus a (i.e., barrier height versus 
length) can be evaluated. 

3.2 For the middle closest critical receiver, prepare a 
cross section through the roadway with uniform horizontal 
and vertical scales, as follows: 



« 



4-24 



* 



SECTION 




B (truck)—' 
B (cars) — 



PLAN with distorted scale 



Roadway 



Barrier 




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4-25 



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4-26 



♦ 



3.2.1 Place the receiver at an appropriate height (5 feet 
above ground level or above floor level for receivers in 
multi-story buildings) . 

3.2.2 Locate the roadway at a distance Dg from the receiver. 
Locate a source at roadway grade level (0 feet) , and at 8 feet 
above roadway grade. Label these as car and truck sources, 
respectively. 

3 o 2 . 3 Include the terrain characteristics between the road- 
way and the receivers. 

3.3 Based on review of the route map prepared under Step 2, 
determine the closest position to the roadway at which a 
barrier could reasonably be placed. Measure the parameters 
L/S and P for truck sources. 

3.4 Refer to the Design Goal Worksheet for the Design Goal 
reduction. Select a trial Design Goal for truck attenuation, 
A (truck) , by subtracting 2 dB from the Design Goal for the 
total attenuation. 

3.5 Since a barrier which just breaks the line-of-sight 
provides about 5 dB attenuation, and each additional foot 
of height provides about an additional 1/2 dB, select a 
trial barrier height as follows: 



H = H L/S + AH (4-2) 



4-27 



where H L / S is the height up to the intersection with the 
line-of-sight to truck sources, and 

AH = (Design Goal - 5) x 2, in feet. (4-3) 

Using this trial height, measure the break in line-of-sight B 
to truck sources. 

Example. Refer to Figure 4-14 again. For the same 
roadway/receiver geometry as in the above 
example, the task is to determine the 
barrier dimensions necessary to provide a 
total attenuation of 8 dB. The first trial 
Design Goal truck attenuation is then 6 dB, 
and the trial barrier height is 

H = 2 + AH, AH = (6 - 5) x 2 = 2 ft. 

Then H is 4 feet, and B is 2 feet since AH 
is approximately equal to B for the geometry 
at this site. 



3.6 Using the values of L/S , B, P, and A (truck) , use the 
Barrier Nomograph to determine the necessary subtended angle 

3.7 Using this subtended angle, determine the attenuation 
for car sources using the appropriate value of B. 

Example (continued). For L/S = 200 feet, B = 2 feet, 

P = 75 feet and A(truck) = 6 dB, 
Figure 4-16 shows the use of the 
Barrier Nomograph to determine a 
subtended angle of 170°. Using 
the angle, and a break in line- 
of-sight B for cars of 7 feet, 
the attenuation of cars can be 
seen to be 9.5 dB (Figure 4-16). 



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4-28 



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4-29 



3.8 Refer to Figure 4-17 to determine the total attenuation 
resulting from the car and truck attenuations defined above. 
Since the total attenuation will depend upon the relative 
contribution of cars and trucks to the total noise level, 
several curves are given in the figure which correspond to 
car versus truck contributions ranging from a car-dominated 
noise exposure (top curve) to a truck-dominated noise exposure 
(bottom curve) . The curves are identified by the difference 
between car and truck noise levels, L(car) - L (truck), as well 
as by the approximate truck mix and closest appropriate speed. 
Using the proper curve and the difference in attenuation for 
car and truck sources, determine the difference between the 
total attenuation and the truck attenuation, and thus the 
total attenuation. If this does not meet the Design Goal, 
adjust the trial truck attenuation by the incremental difference 
by which the total attenuation does not meet its design level. 
Repeat Steps 3.5 through 3.8 until the Design Goals are met. 

Example (continued). Assume that there is a 5% truck mix, 

and the average speed is about 55 mph. 
Then truck noise levels will exceed 
car noise levels by approximately 3 
dB. Refer to Figure 4-17; from the 
above example the difference between 
car d truck attenuation is 9,5 - 6 
=3.5 dB. Using the curve corres- 
ponding to L(car) - L(truck) = 3 dB 
(or truck % = 5 at 55 mph), the 
difference between the total attenua- 
tion and the truck attenuation is 
about 1 dB. Thus the total attenua- 
tion is 6 + 1 = 7 dB, or 1 dB too low; 
this barrier does not provide the re- 
quired attenuation. 

As a second trial, the new truck atten- 
uation Design Goal becomes 6 dB (from 
the first trial) plus 1 dB (the amount 



4-30 



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4-31 



by which the first barrier did not 
meet the Design Goal) or 7 dB. This 
trial attenuation translates to a new 
trial barrier height of 6 feet, with 
B = 4 feet. Figure 4-18 shows that 
this barrier will provide 7 dB atten- 
uation for trucks if it subtends an 
angle of 165°. For this angle, the 
car attenuation (with B = 9 feet) is 
9.5 dB. 

From Figure 4-17, these attenuations 
will provide a total attenuation of 
8 dB. Thus a barrier 6 feet high, 
subtending an angle of 165°, will 
provide the required attenuation. 
The barrier length is 1900 feet 
(based on a subtended angle of 165° 
to a receiver 125 feet behind the 
barrier) . 

3.9 Using the attenuation of truck sources determined above, 
draw a line vertically down from the Barrier Attenuation scale 
through the Angle Subtended chart. Every point on this line 
represents a different potential barrier which will provide 
the same attenuation. For a fixed barrier position, this 
allows a tradeoff of barrier height versus length. 

Based on topographic and community constraints, as well as 
those constraints defined graphically in the route map prepared 
in Step 2, define allowable barrier lengths for the selected 
position. Determine subtended angles for these lengths. 

3.10 For each alternative, work backwards using the nomograph 
to determine the necessary barrier break, and then measure on 
the cross section map to determine barrier height. 



♦ 



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4-33 



Example (continued). As shown on Figure 4-18, by continuing 

the 7 dB truck attenuation line down- 
ward from 165° to 170°, another barrier 
(with break B of 3 feet) can be shown 
to provide the same attenuation. (This 
is not unexpected since these are the 
dimensions of the original barrier 
used above to illustrate the use of the 
Barrier Nomograph, Figure 4-15.) 
Similarly, other barriers could be 
derived from Figure 4-18. 

3.11 Eliminate those alternatives which are clearly impractical. 
Select the combination of height and length which is the most 
reasonable for the community. (The total barrier area for each 
wall option can be determined; the cost of the wall will approx- 
imately scale with total area and this may be used as a rough 
guideline for selecting the most desirable barrier. Also, 
consider the extent of the community in assessing length 
requirements. ) 

3.12 After selection of the desired height and length, compute 
the attenuation for car sources as described above, and verify 
using Figure 4-17 that the total attenuation meets Design Goals. 

3.13 For this barrier wall, define the necessary parameters 
for the appropriate farthest critical receiver from the barrier. 
Use the nomograph to determine attenuation for car and truck 
sources. 

3.14 If the Design Goal for this receiver is not met, modify 
the height or length as necessary to achieve the desired 
attenuation. 



4-34 



• 



♦ 



« 



3.15 If the design of the barrier has been changed, re- 
evaluate the barrier attenuation for the close-in receiver. 

3.16 Evaluate the design for the closest and farthest receivers 
at each end of the community. Adjust barrier length (by using a 
section that bends back if necessary) to provide sufficient sub- 
tended angle. 

3.17 Steps 3.3 to 3.16 have resulted in a barrier design 
located close to the roadway which will satisfy design 
requirements. If right-of-way availability and topographic 
features permit, it would be desirable to determine additional 
barrier locations and designs. Wherever possible, at least two 
other locations should be examined, a position as far from 

the highway as possible, and a position midway. Review the 
topography between the roadway and the receivers. Attempt to 
take advantage of land forms which rise above average terrain 
to minimize the height of wall necessary for construction. 

3.18 For each newly selected location determine L/S and P and 
perform the above analysis from Step 3.5 to yield additional 
designs. 

4-4 Step 4: Identify Additional Barrier Treatments 

In Step 5, specific materials and structural designs will be 
selected for each of the geometrical alternatives defined in 
Step 3. Depending upon local site and community conditions, 
however, various barrier "treatments" may be required. These 
treatments may refer to the application of materials onto the 
barrier, or the incorporation of design features within the 
barrier itself. In order to incorporate the selection of 
these treatments into the barrier design process in Step 5, 
this step identifies those conditions under which these 
treatments will be needed. 



4-35 



4.1 Consider the need for treatments to improve the weathering 
properties of the barrier. Among the factors to be considered 
include knowledge of the weather conditions that might occur at 
the site, previous maintenance experience in the area, and the 
requirements for cleaning the barrier on either the highway or 
community side. 

4.2 Consider the need for aesthetic treatments, based on 
community attitudes and preferences, neighborhood charac- 
teristics, and other local conditions. 



4.3 If vertical barriers are to be constructed on both sides 
of the highway, determine the need for applying acoustically 
absorptive material on the highway side of the barrier, accord- 
ing to the following. If double barriers are not to be used, 
this step as well as Step 4.4 may be skipped. (Note that the 
following methodology is applicable to any vertical walls on 
both sides of the highway, such as a barrier wall on one side 
and a high retaining wall on the other, or the vertical walls 
on each side of a deep cut section.) 

4.3.1 Prepare a cross-section map of the roadway at its closest 
point to the nearest critical receiver. Include the location 
and height of both barriers and the critical receiver location.* 
Indicate on the cross-section map the values of the following 
parameters (refer to the lower left corner of Figure 4-19 for 
a sample sketch) : the separation between barriers, W, in feet; 



*If several sets of parallel barrier alternatives are under 
consideration, perform this analysis using the barriers 
closest to the roadway, that is, those barriers with smallest 
separation between them. 



• 



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4-36 




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4-37 



the barrier height, H, in feet; the horizontal distance from 
barrier to receiver, D B , in feet; and the receiver height 
above road level, H R , in feet. 

4.3.2 As shown in the figure, locate the noise source at the 
center of the roadway eight feet above ground level. Draw the 
sight line from this source over the near barrier; label the 
height above road level at which this sight line intersects 
the receiver location as H N . 

4.3.3 As shown in the figure, locate the first ground image 
source eight feet below road level at a distance «• from the 
far barrier. Draw the sight line from this source over the 
top of the far barrier until it intersects the receiver loca- 
tion. Label the height above road level of this intersection 
as H F . 

4.3.4 Determine H N and H F by measurement and indicate on the 
drawing. 

4.3.5 Determine the region in which the receiver is located: 
if H R is less than H, the receiver is in Region I. If H R is 
greater than H but less than H N the receiver is in Region II. 
If H R is greater than H N , the receiver is in Region III. Pro- 
ceed as follows for receivers in Regions I or II; skip to 
Step 4.3.9 for receivers in Region III. 



4-38 



• 



< 



Example. Figure 4-20 shows a section through a highway with 
parallel barriers, indicating values of the follow- 
ing parameters: W = 116 feet, D B = 112 feet and 
H = 16 feet. By measurement the values of H N and 
Hp are determined to be 30 feet and 116 feet re- 
spectively. 



4.3.6 Using the Barrier Nomograph (Figure 4-13) , determine 
the attenuation provided by the near barrier for the eight 
foot source in the center of the road for two heights : the 
actual receiver height, and the height corresponding to road - 
way level (i.e., H = ) . 

4.3.7 The degradation in barrier performance ABAR may be 
determined using the nomograph in Figure 4-19. 

4.3.7.1 Starting at the lower right corner of the figure, draw 
a straight line between the D_, and W scales. 

4.3.7.2 Draw a straight line from the A B scale for the barrier 
attenuation corresponding to a receiver height of zero feet 
above road level, through the intersection of the first line 
with the pivot line, and continue to Turn A. 

4.3.7.3 Project this line vertically upward to the curve 
labeled NRC = 0.05, which corresponds to a nearly perfect 
reflecting surface. Turn left and project horizontally to 
Turn B. 



4-39 



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4.3.7.4 If the receiver is located in Region I proceed as 
follows. If the receiver is located in Region II skip to 
4.3.7.8. 

4.3.7.5 Refer to the grid on the left of the figure. Project 
upwards vertically from the H R scale to the curve labeled 

NRC = 0.05. Turn right and project horizontally to Turn C. 

4.3.7.6 Draw a straight line between the points determined 
on the Turn B and Turn C lines. 

4.3.7.7 Read the value of ABAR where this line crosses the 
center scale. This value is the barrier degradation for a 
receiver height Hr. Skip to Step 4.3.8. 



Example (continued). For a receiver height of 5 feet, the 

receiver is in Region I. The Barrier 
Nomograph is used to determine the 
attenuation from the near barrier, 
using L/S = 170 feet, P = 58 feet, 
B = 10 feet for H R = 0, and B = 9 
feet for Hr = 5. From the nomograph, 
the attenuation is 12.5 dB and 11.5 dB 
for and 5 foot high receivers, 
respectively. The steps involved in 
determining ABAR are shown in Figure 
4-21, numbered sequentially (solid 
line). For the 5 foot receiver, 
ABAR is 4.5 dB. 



4.3.7.8 Refer to the grid on the left of the figure. For a 
receiver in Region II use the barrier height H as the value 
of H R ; project vertically upwards from the H R scale to the 
curve labeled NRC = 0.05. Turn right and project horizontally 
to Turn C. 



4-41 




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4-42 



4.3.7.9 Draw a straight line between the points determined 
on the Turn B and Turn C lines. 

4.3.7.10 Read the value of ABAR where this line crosses the 
center scale. For a receiver in Region II , the barrier degra- 
dation is less than or equal to this value read from the nomo- 
graph for a receiver height equal to the height of the barrier 
H. 

4.3.7.11 To determine the barrier degradation for the actual 
receiver height, construct a graph of ABAR versus H_, using the 
grid provided in Figure 4-22. Plot the following two points: 
H R = H, ABAR = the value determined above in 4.3.7.10; and 

H R = H F , ABAR = 0. Draw a straight line between these two 
points. Read ABAR from the graph corresponding to the actual 
value of H R . 

Example (continued). For a receiver located 25 feet above 

road level (therefore in Region II), 
ABAR is first determined for a re- 
ceiver height equal to barrier height, 
16 feet. These steps are shown in 
Figure 4-21 (dashed line), resulting 
in ABAR =6.5 dB. In Figure 4-23, 
the values Hp = 116, ABAR = 0, and 
H = 16, ABAR =6.5 are plotted. The 
value of ABAR for Hr = 25 is read from 
the graph as 6 dB. 

4.3.8 In Step 4.3.7, the degradation in barrier performance 
relative to receivers in Regions I and II for truck sources 
was determined. Determine the noise reduction for the barrier 
for truck sources by subtracting ABAR from the barrier attenua- 
tion for trucks, determined in Step 4.3.6 for the actual receiver 
height: 



4-43 



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• 



FIGURE 4- 22 Grid to Determine A BAR for Receivers in 
Region II. 



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Height above Roadway Grade, Feet 



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FIGURE 4-23 Use of Grid to Determine ABAR. 



4-45 



NR = A B (trucks) - ABAR (trucks) (4-4) 

To a first approximation, this noise reduction is appropriate 
to cars as well as trucks, and therefore is the net noise re- 
duction for the barrier. 



Example (continued). For the 5 foot receiver, the near 

barrier truck attenuation is 11.5 
dB. Thus, the net noise reduction 
for both cars and trucks is 11.5 - 
4.5 = 7 dB. 



4.3.9 In Region III, the receiver has a clear view of the 
highway, and the near barrier thus provides little or no 
attenuation. The maximum effect of the double walls will 
be to increase the unshielded level at the receiver by 3 dB. 
This effect decreases to at a height H p . 

4 . 4 The effects of the double wall configuration can be 
reduced (or eliminated entirely) by increasing barrier 
height (and thereby increasing the attenuation) and/or by 
decreasing the reflected sound levels by applying absorptive 
treatments to the wall surfaces. If ABAR is within 3 dB, 
increasing wall height may be the most practical approach. 
For higher degradations the use of absorptive materials may 
be more desirable. 

4.4.1 If an increase in barrier height is considered, note 
that ABAR will increase as A B increases (but not as rapidly) . 
Choose a barrier height to give an additional attenuation 
somewhat greater than ABAR. Determine the actual barrier 



4-46 



• 



• 



attenuation using the Barrier Nomograph (Figure 4-13) and 
then re-evaluate ABAR with the Parallel Barrier Nomograph 
(Figure 4-19) to verify that the net noise reduction meets 
Design Goals. 

4,4.2 If it is desired to use absorptive treatments, the 
acoustical benefits can be determined as a function of the 
noise reduction coefficient, NRC. The absorptive materials 
presented in later steps have NRC values of 0.5 or better. 
To judge the benefits of using such materials, re-evaluate 
the degradation of barrier performance ABAR using Figure 4-19 
for various noise reduction coefficients. (Note that ABAR = 
for NRC =1.0) Figure 4-24 indicates the improvement in 
Region III. Determine the minimum NRC which would reduce 
ABAR to within desirable limits. 



Example (continued). Figure 4-25 shows the benefits of 

using absorptive treatments having 
NRC values on the order of 0.8. 
For both the 5 foot (Region I) and 
25 foot (Region II) receivers, 
ABAR is reduced to within 0.5 dB. 
For a receiver in Region III, the 
increase in unshielded level is 
also within 0.5 dB. 



4.5 If the noise barrier is to be located within 30 feet of 
the traveled way, a safety barrier may be appropriate. Such 
a barrier could be placed in front of the wall, or integrated 
within the wall construction itself. Consideration should be 
given to local requirements dealing with safety, and to previous 
experience and accident records for similar configurations and 
for the particular roadway site under consideration. 



4-47 



• 



FIGURE 4-24 EFFECTS OF BARRIER REFLECTIONS FOR RECEIVERS IN 

REGION III (H N < H R < H F ) 

NRC Increase in Unshielded Level, dBA 



0.05 


3.0 


0.1 


2.5 


0.3 


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1.0 


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4-49 



4-5 Step 5: Select Design Options 

In Step 3, alternative barrier locations were selected, and 
the necessary height and length of the barrier determined 
for each of these alternatives. In this step, specific 
design options are selected for each barrier location. 

5.1 Refer to the Design Option Worksheet (Figure 4-26.) 

The first column labeled "Material" is to be used to identify 
the basic material of which the barrier might be constructed. 
Each of the next columns is to be used for a single geometrical 
alternative. Fill in the three basic dimensions for each al- 
ternative in the column heading: the barrier position P_. 
represented by the distance from the barrier to the edge of 
the roadway; the barrier height H; and the barrier length L. 
Each row of the Worksheet then corresponds to one or more 
specific barrier designs using a particular material for at 
least one of the alternative locations. 

5.2 Among those materials commonly used for noise barrier 
walls are concrete, masonry block, steel, and wood. Earth 
berms are also used either alone or in combination with one 
of the above barrier walls. Appendices A and B provide 
reference drawings with design details for each of these 
materials. Select appropriate materials* for potential use. 
List the materials in the left column of the Worksheet. 

5.3 If it is desirable to consider other materials for con- 
struction, Figure 4-2 7 provides a more comprehensive listing 
of potential barrier materials (including materials used in 



*Note that with the exception of the wood barriers, all the 
barriers included in the reference drawings have transmission 
losses of 25 dB or better. Depending on the wood used, the TL 
of the wood barrier would be in the range from 22 to 26 dB. 



4-50 



• 



• 



• 



• 



FIGURE 4-26 
DESIGN OPTION WORKSHEET 

LOCATION NUMBER 



• 





Position / 


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MATER 1 AL 


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No. 2 




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Wind Loading 


Safety Barrier 


Aesthet ics 


Absorpt ion 


Weather i ng 


Other Comments 




DES 1 GN CODE 


DESCR I PT I ON 


NOISE REDUCTION 
LIMITED ? 































































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4-55 



the reference drawings) . In selecting additional materials 
from this list, consideration must be given to transmission 
loss characteristics; the transmission loss of each material 
is shown in the figure. Note that some materials (and es- 
pecially wood materials) are prone to develop openings or 
gaps in the barrier through weathering. The effect of open- 
ings on the TL of the barrier can be determined from Figure 
4-2 8, which has been developed for wood materials. (For other 
materials, use the curve with the closest TL for 0% open area.) 

5.4 Figure 4-2 9 indicates the noise reduction resulting from 
use of a material as a function of its transmission loss (based 
on the physical properties of the material as well as the pre- 
sence of openings) and the attenuation if there were no trans- 
mission through the barrier. For each material considered, 
compare the transmission loss determined from Figures 4-2 7 
and 4-2 8 with the attenuation for the barrier (determined in 
Step 3) to evaluate the maximum noise reduction achievable. 
Eliminate from further consideration those materials which 
would seriously degrade barrier performance by transmission 
through the barrier. List acceptable materials on the Worksheet. 



Example. Consider the use of one-half versus two inch 
tongue and groove fir boards for a proposed 
barrier. Figure 4-27 indicates TL values of 
17 and 24 dB, respectively. If the barrier 
has been designed to provide an attenuation 
of 10 dB, Figure 4-29 shows that use of one- 
half inch fir will result in a noise reduc- 
tion of about 9 dB, while two inch fir will 
result in a noise reduction of nearly 10 dB. 
In this case the factor of two in cost to use 
two inch rather than one-half inch boards may 
not be justified. 



* 



♦ 



4-56 



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10 




THICKNESS 

OF LUMBER 

( inches ) 




2 4 6 8 

PERCENTAGE OF BARRIER SURFACE THAT IS OPEN 



10 



FIGURE 4-28 Effect of Barrier Openings on TL 



4-57 



FIGURE 4-29 NOISE REDUCTION OF A BARRIER AS A 
FUNCTION OF ITS TRANSMISSION LOSS 



Attenuation, dB 


TRANSMISSION LOSS, dB 


10 


15 


20 


25 


30 


5 


3.8 


4.6 


4.9 


5.0 


5.0 


6 


4.5 


5.5 


5.8 


6.0 


6.0 


7 


5.2 


6.4 


6.8 


6.9 


7.0 


8 


5.9 


7.2 


7.7 


7.9 


8.0 


9 


6.5 


8.0 


8.7 


8.9 


9.0 


10 


7.0 


8.8 


9.6 


9.9 


10.0 


11 


7.5 


9.5 


10.5 


10.8 


11.0 


12 


7.9 


10.2 


11.4 


11.8 


11.9 


13 


8.2 


10.9 


12.2 


12.7 


12.9 


14 


8.5 


11.5 


13.0 


13.7 


13.9 


15 


8.8 


12.0 


13.8 


14.6 


14.9 


16 


9.0 


12.5 


14.5 


15.5 


15.8 


17 


9.2 


12.9 


15.2 


16.7 


16.8 


18 


9.4 


13.2 


15.9 


17.2 


17.7 


19 


9.5 


13.5 


16.5 


18.0 


18.7 


20 


9.6 


13.8 


17.0 


18.8 


19.6 



♦ 



• 



4-58 



» 



» 



However, if the barrier has been, designed to 
provide 15 dB attenuation because of more 
stringent noise reduction goals, Figure 4-29 
shows noise reductions of about 12.5 and 14.5 
dB for one-half inch and two inch boards 
respectively. In this case the one-half inch 
boards degrade barrier performance by 2.5 dB, 
which may not be an acceptable situation. 

Assume that with time a 2% open area will 
develop if tongue and groove boards are not 
used in the construction of the barrier. 
Figure 4-28 shows that the TL values are 
reduced to 14 and 16 dB for the one-half inch 
and two inch boards, respectively. Figure 
4-29 indicates a compromise in barrier perfor- 
mance of about 1 dB for a barrier designed for 
10 dB attenuation, and 3 dB for a barrier 
designed for 15 dB attenuation. This illus- 
trates that (1) openings can seriously degrade 
a barrier's potential for noise reduction, and 
(2) openings tend to equalize the TL of different 
thickness materials, so that if an opening cannot 
be avoided there is little acoustical benefit in 
using a heavier material. 



5.5 The Design Option Worksheet may be considered as a matrix 
of possible barrier designs. If a barrier could be constructed 
from each of the materials listed in the first column for each 
of the barrier locations, then the number of possible barrier 
designs would be the number of locations times the number of 
materials, assuming only one specific design per material. 
If it is desirable to evaluate more than one design for a 
particular material, then the number of potential designs 
would increase accordingly. At this point it would be 



• 



4-59 



appropriate to eliminate those defiant which could not be 
constructed at one of th« alternative locations. The 
primary reason that this mifht happen would be the amount 
of land required for the construction of an earth berm. 
Figure 4-30 indicates the width required for different 
height earth berms as a function of tha alope. This table 
can be used to eliminate those locations which would not 
accommodate earth berms, if this type of barrier is one of 
the designs under consideration. Eliminate other material/ 
location options which are impractical. 

5.6 In addition to the basic construction details shown 
in the reference drawings in Appendices A and B, for each 
material several "additional treatments" ara detailed. 
These treatments may be used to upgrade the weathering 
properties of the barrier, improve tha visual appearance 

of the barrier, or provide sound absorption. The weathering/ 
aesthetic treatments are detailed on the reference drawings 
for the particular barrier for which they apply; the absorption 
treatments are detailed separately in Appendix C. Figure 4-31 
provides an index to the various treatments. Note that under 
the broad category of "treatment" is included such diverse 
items as painting, use of different types of maaonry blocks, 
application of stucco, wood or sheet metal facings, and land- 
scaping. 

5.7 Each complete barrier design will include a basic barrier 
construction using a particular material; weathering/aesthetic 
treatments if appropriate; a safety barrier if warranted; and 
absorption treatments if necessary. For ease of tabulation 



♦ 



4-10 



• 



I 



'It/K 4-30 

APPROXIMATE IISKT-OMAY MCESSAIV FOR Ittt CONSTMTIlM 



» 







Btrn Httfht 






X of Slop* 


S 


10 


11 




4:1 


$v 


♦2' 


Ml' 


172' 


3:1 


It' 


72' 


102* 


132' 


2:1 


32' 


52' 


72' 


I2 1 



» 



«-«i 



FIGURE 4-31 
INDEX TO REFERENCE DRAWINGS 



Appendix A 

Concrete 

Exposed Aggregate 
Sandblast 
Board Form 
Wood Form 
Reinforcing Bar 
Rubber Mat 
Bomanite 
Integral Color 
Paint 

Masonry 

Vertical Scored 
6" Slump 
4" Slump 
Combed 
Split Face 
Integral Color 
Paint 



Steel 



Sheet Metal Trim 

Sheet Metal Trim and Wood 

Sheet Metal Trim and Stucco 

Paint 

Weathering Steel 

Wood 

Plywood Facing 

Wood Battens 

Preservative Treatment 

Paint 

Stain 

Earth Berm 

2:1 Slope 
3:1 Slope 
4:1 Slope 
Landscape 



» 



Design Code 


Page Number 


C- 


C-1,2 


1* 


C-3 


2* 


C-3 


3* 


C-3 


4* 


C-3 


5* 


C-3 


6* 


C-3 


7* 


C-3 


8 


C-3 


9* 


C-3 


M- 


M-1,2 


1 


M-3 


2 


M-4 


3 


M-4 


4 


M-4 


5 


M-4 


6 


M-3, M-4 


7* 


M-3, M-4 


S- 


S-l 


1* 


S-2 


2* 


S-3 


3* 


S-4 


4* 


S-l 


5 


S-l 


W- 


W-l 


1* 


W-2 


2* 


W-3 


3 


W-l 


4* 


W-l ,2 


5* 


W-l, 2 


B(2)- 


B-l 


B(3)- 


B-l 


B(4)- 


B-l 


1 


B-l 



• 



4-62 



• 



> 



I 



FIGURE 4-31 

INDEX TO REFERENCE DRAWINGS (cont'd) 

Design Code Page Number 
Appendix B 

Elevated Steel Barrier ES- ES-1 

Paint 1* ES-1 

Weathering Steel 2 ES-1 

Elevated Wood Barrier EW- EW-1 

Preservative Treatment 1 EW-1 

Paint 2* EW-1 

Stain 3* EW-1 

Appendix C 

Absorption Treatments 

Resonant Cavity Blocks al A-l 

Paint (1)* A-l 

Wood Fiber Planks a2 A-2 

Vermiculite Aggregate a3 A-3 

Glass Fiber/Wood Facing a4 A-4 

Paint (1) A-4 





al 




(1)* 




a2 




a3 




a4 




(1) 




a'5 




(1) 




(2) 


Barrier 


a6 


Barrier 


a7 



Glass Fiber/Metal Siding a5 A-5 

Paint (1) A-5 

Weathering Steel (2) A-5 

Glass Fiber/Wood on Steel Barrier a6 A-6 

Glass Fiber/Metal on Steel Barrier a7 A-7 



*These treatments are applied to one side only. If application on both 
sides is desired, use Code twice. 



• 



4-63 



and evaluation, each barrier design will be represented by 
a barrier "Design Code," with descriptors corresponding to 
the various constructions and treatments included in the 
complete design. The Design Code will have four components 
separated by hyphens, as follows: X - i,i,i - S - aj (i) . 
Each component corresponds to one of the components of the 
barrier design: the X refers to the basic material used to 
construct the barrier; the i's refer to various weathering/ 
aesthetic treatments; the S refers to the use of a safety 
barrier; and the aj refers to a specific absorption treatment 
(with additional treatments represented by the (i) following 
the aj ) . Figure 4-32 provides further details concerning the 
Design Code format. The various Design Code components are 
defined in the reference drawing index, Figure 4-31. 

5.8 Review the reference drawings for each of the basic 
barrier materials under consideration, and select appropriate 
treatments for each. For barrier materials not included in 
the reference drawings, develop corresponding treatments as 
necessary to meet local conditions (and devise appropriate 
design codes) . 

5.9 For each empty cell in the location alternatives/materials 
matrix on the Design Option Worksheet, develop complete designs 
and enter the Design Codes as appropriate. At the bottom of 
the Worksheet, provide a brief narrative description of each 
unique design. 

5.10 Note on the bottom of the Worksheet those designs which 
do not provide the Design Goal Noise Reduction. This will 
occur if (a) the height and/or length of the barrier are not 
large enough to provide the necessary attenuation; (b) the 



4-64 



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4-65 



transmission loss of the barrier material is not high enough; 

(c) the absorptive properties of the barrier surface are not 

sufficient to reduce reflections from a double wall configura- 
tion. 

Example. Figure 4-33 shows a completed Design Option Worksheet. 
Barrier designs are listed for three locations: 15, 
60 and 100 feet from the roadway. The barrier dimen- 
sions at each location have been selected to provide 
the required noise reduction. Barrier designs are 
shown for concrete, masonry and wood materials, and 
for earth berm configurations. Note that because of 
space requirements, a berm is only possible at Loca- 
tion 2. Also note that designs are given for a berm 
alone, and for a berm/wall combination. For all 
barriers at Location 1, a safety barrier has been 
included in the design. 

4-6 Step 6: Define Cost Factors 

6.1 Refer to the Cost Factor Worksheet, Figure 4-3 4. Enter 
in the first column each design code listed on the Design 
Option Worksheet (that is, each filled-in cell on the Design 
Option Worksheet will have a separate listing on this Worksheet) . 
Also enter the wind loading requirements on top of the Worksheet. 

6.2 Enter in the next three columns the location alternative 
number and the corresponding height and length of each barrier 
design. 

6.3 cost factors are to be entered in each of the next four 
columns, corresponding to the cost of the basic construction, 
the weathering and aesthetic treatments, the construction of 
a safety barrier where necessary, and the use of absorptive 
linings where necessary. For each letter or numeral in the 
design code, a separate cost factor should be listed. 



4-66 



♦ 



DESIGN OPTION WORKSHEET 



LOCATION NUMBER 





Pos i t i on / 


Height /Length 




MATER 1 AL 


No. 1 


No. 2 


No. 3 


IS* 1 13 1 lotb 


£0 / /fr /^OO 


/60 / /5" /?<3d6 


CotJcfcere 


^-V.F-5 


C -^,^.? 


£-2,2.? 


<■ -3.3; 1-5 


C-3,3.* 


<^3.af 








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M-3^-5" 


M'3 y £ 


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Cv» 6 L> 


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u/ - ^ ^ - 5 


w-«,^ 


\AJ -*f f H 








e^e-i^ 




6^>-/ 






B^-l; M-3,6 










Wind Loading 


^O "*%* Safety Barrier f^^- £oC No. 1 


Aesthet ics 


VES Absorption Nto 


Weather i ng 


V^^ Other Comments 






DESIGN CODE 


DESCRIPT ION 


NOISE REDUCTION 
LIMITED ? 


c~ia.% 


eoKtceere /S ANBlMt/ 'HTectzAL. c*loG. 


Wo 


^-3,3,? 


c*Mc#e7&/BoAG.D Fo#M / /NTCOzAL ^oane 


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MAS om^ / 4 "» Sl wMP / iNt couf. ~ $* WH J 


v n v 




J 











FIGURE 4-33 Use of Design Option Worksheet 



4-67 



FIGURE 4-3A 
COST FACTOR WORKSHEET 



Wind Loading 



Des ign 
Code 


Loc. 

No. 


Ht. 
Ft. 


Length 
Ft. 


COST FACTORS 


TOTAL COST 


Bas ic 


Weather/ 
Aesthet. 
Treatmts 


Safety 
Barr ier 


Absorptive 
Treatments 


TOTAL 



















































































































































































































































































































































































































































































































































































• 



• 



• 



4-FR 



6.3.1 The cost factors are found on the various reference 
drawings in Appendix A for the basic constructions and weather/ 
aesthetic treatments (and similarly in Appendix B for barriers 
on elevated structures) , and in Appendix C for absorption treat- 
ments. For a particular design, the cost factor is a function 
of height of the barrier, and either the wind loading requirement 
of the wall or the slope of the earth berm. The correct cost 
factor is found by first selecting the appropriate wind loading 
(or slope) , and then choosing the proper height. Note that the 
various letters and numerals of the design code are indicated 
in block form on the reference drawings just under or above 
the appropriate cost factor. 

Example. Consider a 15 foot wall designed for 30 pounds per 

square foot wind loading. The cost factor for design 
option C-2,2,8 is determined as follows. From the reference 
drawings for concrete barriers, the cost factor for 
the 15 foot basic concrete wall designed for 30 pounds 
per square foot is 88.15. The cost factors for treat- 
ments C-2 and C-8 are 3.11 and .35 respectively for 
15 foot height. Thus the cost factor for the treat- 
ments is 3.11 + 3.11 + .35 = 6.57. The total cost 
factor for the wall is 6.57 + 88.15 = 94.72. 

If a barrier height is used other than 5, 10, 15, or 20 feet 
the correct cost factor can be found by interpolation between 
the cost factors for the next lowest and next highest barriers. 
Figure 4-35 provides a grid for performing this interpolation. 
On the bottom horizontal axis plot the value of the cost factor 
for the next lowest wall. Plot the cost factor for the next 
highest wall on the top axis, and draw a line connecting these 
two points. The cost factor for the design wall can then be 
read directly from the graph corresponding to the actual height, 
as read on the vertical axis. 



4-69 



• 



4-> 
00 
0) 

O O) 

—I O) 



> 
O 



>> 

s- 
o 

<Li 
+-> 
fO 



CD CT1 



50.00 100.00 

Cost Factor 



150.00 



♦ 



F IGURE 4-35 Grid to Determine Barrier Cost Factor 



4-70 



• 



Alternatively, the interpolation can be done more precisely 
as follows. If H and CF represent "height" and "cost factor," 
respectively, and the subscript + represents the 5-foot height 
category above the design wall (and - represents the height 
category below the design wall) , then the desired cost factor 
CF for wall of height H is 



CF = CF - (H - H) x (CF - CF ) (4-5) 

+ + + 



5 

Example. An 18-foot wooden wall basic cost factor is de- 
termined by plotting the 15-foot and 20-foot 
cost factors, and interpolating, as shown on 
Figure 4-36. Alternatively, the interpolation 
may be performed according to equation (4-5): 

cost factor = 111.55 - 2x (m.55- 64.69) . 

5 



6.3.2 If a safety barrier is included in the design, refer 
to Figure 4-37 for cost factors for three types of barriers. 
Select the desired barrier type and enter the corresponding 
cost factor. 

6 3 . 3 For barrier designs based on the materials listed in 
Figure 4-27, cost factors are provided on a square foot basis. 
Note that the cost factors refer to the wall material only, 
and do not include the costs of structural support (except for 
the concrete and masonry materials) . Cost estimates for the 
total wall construction should be .developed using the wall 
material costs in Figure 4-2 7. 



4-71 



• 



CF for 20' wall = 111.55 



to 

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50.00 100.00 

Cost Factor 



150.00 



♦ 



FIGURE 4-36 Use of Grid to Determine Cost Factor. 



4-72 



♦ 



FIGURE 4-37 SAFETY BARRIER COST FACTORS 

Barrier Type Cost Factor 

Cable* 4.80 

Metal Beam 19.97 

Concrete 12.08 



*Not recommended for roadway-to-barrier 
distances less than sixteen (16) feet. 

Source: Based on data in Reference 4-3, 



4-73, 



6.4 Sum the individual cost factors and enter the total in the 
next column, for each barrier design. 

6.5 Refer to Figure 4-38 for relative cost indices for major 
cities in the United States in 1975. Determine the cost index 
for the city closest to the highway project. Determine from 
the Bureau of Labor Statistics the local cost index for the 
current year and the local cost index for 197 5. The total 
cost of the barrier can be estimated as follows: 

Total Cost = Total Cost Factor x Barrier Length x 

City Cost Index x Current Cost Index (4-6) 

100 1975 Cost Index 

Compute and enter the total cost of each barrier option. 

Example. The various design options on Figure 4-33 are 
translated into costs in Figure 4-39, a sample 
Cost Factor Worksheet. The total cost factors 
are converted to total costs assuming that the 
site is located near a city with a relative 
city cost index determined from Figure 4-38 of 
95. It is also assumed that this city had a 
cost index in 1975 of 106, and at the time of 
construction has a cost index of 121.9 
(equivalent to a 15% inflation). For the 
design C-2,2,8 above, the total cost is 
(rounded to the nearest hundred dollars): 

94.72 x 8000 x y^| x ^^- = $827,900 

6.6 These total costs can be used to compare all of the designs 
with one another. (The cost factor concept can also be used for 
one specific design to evaluate the cost/benefit of modifications 
to that design, such as increasing the height by a few feet, in- 
creasing or decreasing the length, etc.) 



• 



• 



4-74 



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COST FACTOR WORKSHEET 



Wind Loading 3d /$ 



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FIGURE 4-39 Use of Cost Factor Worksheet 

4-76 



♦ 



4-7 Step 7: Assess Functional Characteristics 

In addition to its noise reducing properties, there are several 
other characteristics of the barrier which should be evaluated. 
In this step these non-acoustical characteristics are rated. 

7.1 Refer to Figure 4-40, the Design Evaluation Worksheet. 
List in the left two columns the design code and location 
number for each barrier option, as listed in the Design Option 
Worksheet. 

7.2 Along the top of the Worksheet, under the heading "Func- 
tional Assessment," several items are listed which refer to 
the non-acoustical characteristics, or the functional "perfor- 
mance" of the barrier: aesthetics, durability, ease of mainte- 
nance, safety, ease of snow removal, and community acceptance. 
There is also space for inclusion of other characteristics which 
may be important, based on local conditions. 

7.3 For each of these categories, assign a +, 0, or - rating 
for each design option. Use of a + rating implies better than 
average performance for a barrier design in a particular cate- 
gory, and similarly a - rating is indicative of less than average 
performance. Establishment of rating criteria is necessarily 
site dependent, and must be determined by the designer based on 
state and local standards, past experience, knowledge of the 
community and citizen input. The following guidelines may be 
useful. 

7.3.1 The evaluation of aesthetics of noise barriers must, by 
its nature, be qualitative rather than quantitative. In this 
area, the judgment of the highway designer as to the local con- 
ditions and the appropriate visual treatment of the wall with 
respect to adjoining land use will be a primary consideration. 



4-77 



FIGURE 4-40 
DESIGN EVALUATION WORKSHEET 



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• 



4-71 



♦ 



7.3.2 Physical durability considerations include the durability 
of the barrier material to the effects of moisture, temperature 
changes, wind, and the effects of automotive exhausts, dirt, sand, 
and salts used in snow removal. 

7.3.3 Factors to assess the ease of barrier maintenance are 
threefold. First is the evaluation of the effect of an impact 
on the barrier wall from a maintenance standpoint which (with 
the exception of concrete and concrete masonry units) will 
require replacement of portions of the barrier. This mainte- 
nance factor can be considered proportional to initial installa- 
tion costs. Second are routine maintenance considerations such 
as repainting of a surface considering the normal lifespan of 
paint. The third maintenance consideration is the ease of clean- 
ing the material, which is related to the porosity of the surface 
to be cleaned. 

7.3.4 Safety factors are concerned primarily with the relative 
safety of the walls in an impact situation. For example, a wall 
with a facing material which can be dislodged and become a missile 
is considered less safe than a solid concrete wall or an earth 
berm. (It is assumed that the barrier location has been selected 
with safety considerations in mind [Step 2.3].) 

7.3.5 Snow removal considerations are with regard to sufficient 
room for snow storage initially, and then easy removal without 
disruption of traffic flow. 

7.3.6 If community input has been incorporated throughout the 
design process, assessment of barrier acceptability should be 
fairly straightforward. 



4-79 



Example. Figure 4-41 illustrates the use of the Design 
Evaluation Worksheet, for the design option 
examples above. 



4-8 step 8: Select Barrier 

8.1 In the column labeled "Total Cost" on the Design Evaluation 
Worksheet, enter the total estimated cost from the Cost Factor 
Worksheet for each barrier option. 

8.2 In the last column indicate whether the Design Goal Noise 
Reduction has been achieved by each design option. Enter quali- 
fying comments as appropriate. 

8.3 Based upon the acoustical performance, total cost, and 
functional characteristics of each barrier, select the design 
option most appropriate to local conditions. (In evaluating 
the functional characteristics, it should be remembered that 
for a particular highway site, some of the characteristics 
may be much more important than others . ) 

4-9 step 9: Design Barrier 

9.1 After selection of a specific design, it is desirable 
to "optimize" the barrier height and length by taking into 
consideration those factors which were neglected in the 
original assessment, such as terrain features in the vicinity 
of the site, and variations in the highway configuration and 
traffic flow. It is recommended that the TSC computer program 



• 



♦ 



4-80 



♦ 



DESIGN EVALUATION WORKSHEET 







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4-81 



be used to guide the refinement of the barrier dimensions. 
This would involve first computing accurately the attenuation 
provided by the selected approximate barrier design, and 
then adjusting the dimensions of various sections of the 
barrier, based on the resulting noise levels at critical 
receivers along the route. While this process may take 
several iterations before a complete barrier design is 
developed which provides the desired attenuation at all 
receivers, it is certainly worthwhile to undertake in light 
of the potential savings of barrier construction costs for 
an overdesigned barrier, as well as the potential benefits 
of avoiding an underdesigned barrier. 

9.2 While the TSC methodology can make an accurate assess- 
ment of barrier attenuation for a specific design, it does 
not consider the effects of barrier transmission or multiple 
reflections. If the transmission loss of the selected barrier 
material is within 10 dB of the computed barrier attenuation, 
or if double parallel barriers are present, their effects on 
the total noise reduction of the final barrier design should 
be assessed as described in Steps 5.4 and 4.3, respectively. 
(Note that in assessing the effects of multiple reflections, 
separate values of ABAR should be determined for truck and 
car sources, to provide an accurate estimate of the net noise 
reduction of the barrier. To use the Parallel Barrier 
Nomograph for cars, Hs = feet for both the source and ground 
image source.) 



4-82 



• 



• 



♦ 



9.3 If the selected design option involves one of the 
reference drawings, review the particular drawing to ensure 
that the assumptions used in the design calculations are 
appropriate for the site under consideration. Adjust the 
design details on the reference drawings as necessary for 
specific conditions at the site. 

9.4 If the selected design option is based upon a material 
not included in the reference drawings, the reference draw- 
ings may be used to provide guidance in the detailed design 
of the barrier. 



4-83 



CHAPTER 5 
BARRIER DESIGN EXAMPLES 

Examples of the design procedure in Chapter 4 are presented 
in this chapter. The first example involves a rather simple 
highway/community configuration, for which a single uniform 
barrier is required. The second example considers the effects 
of parallel barriers. Finally, the third example deals with 
a more complicated configuration which requires a segmented 
barrier design. 

For additional examples refer to Appendix D, in which the 
design procedure has been applied to five actual highway 
sites where barriers have been constructed. 

5-1. Basic Example of Barrier Design 

Figure 5-1 shows a typical community adjacent to an at-grade 
highway. Assume high volume, high speed traffic flow on the 
highway with a 5% truck mix. Based on noise level projections 
determined using the 117/144 methodology, critical receivers 
have been selected in pairs at each end of the community and 
in the middle of the community. Each pair consists of a 
receiver close-in to the highway, and a receiver farther out 
for whom an L, n criterion of 70 dBA is exceeded. The six 
selected receivers are indicated in the Figure, with the 
projected pre-barrier noise levels and the near and far lane 
distances shown for each receiver. Note that although 
Receiver 6 has a projected level of 69.5 dBA, it is included 
as a critical receiver in anticipation of a possible increase 
in noise level resulting from potential loss of ground absorp- 
tion effects when the barrier is installed. (Also note that 



5-1 




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5-2 



noise levels are not uniform along the back of the community 
because of differences in shielding provided by intervening 
rows of houses: Receiver 2 experiences essentially no benefits 
from this shielding, Receiver 4 benefits from two complete rows, 
and Receiver 6 benefits from house shielding for only the left 
portion of the highway.) 

With this information, Figure 5-2 illustrates the use of the 
Design Goal Worksheet. Note that Figure 4-3 has been used to 
determine A G , and that in the absence of other shielding ele- 
ments, A_ is added to the Insertion Loss to yield a Design 
Goal noise reduction. 

For this example the community is assumed to be at road level 
elevation, and the vertical configuration of the highway is 
assumed to be unchanged along its length adjoining the community 
There are no intersecting ramps or streets in the vicinity of 
the community. A wind loading requirements of 30 pounds/square 
foot is assumed to be appropriate for the area. 

Figure 5-3 shows a cross section through the highway and 
middle column of receivers (including Receivers 3 and 4) 
at Station 100. On the figure, car and truck sources are 
located at the equivalent lane distance from Receiver 3. A 
trial barrier location is established three feet beyond the 
highway shoulder; L/S and P are indicated on the figure. For 
a Design Goal noise reduction of 10.5 dB, a trial truck atten- 
uation of 8.5 is chosen, and AH = (8.5 - 5) x 2 = 7 feet. Thus, 
H = 14 feet and B = 7 feet. Using these parameters, the 
Barrier Nomograph is used to determine that a subtended angle 
of 163° is required (see Figure 5-4) . 



5-3 





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5-6 



For this barrier, B = 12 feet for car sources. Applying 
the Barrier Nomograph shows that the car attenuation is 
10 dB (see Figure 5-4). Referring to Figure 4-17, it can 
be seen that for a 5% truck mix at 55 mph, with a 1.5 dB 
difference in car and truck attenuations (10 - 8.5 = 1.5), 
the total attenuation is only 0.5 dB above that for trucks 
in this case. Thus the total attenuation is 9 dB, which is 
1.5 dB too low. 

On this basis a new trial height is evaluated based on a 
trial truck attenuation of 8.5 + 1.5 = 10 dB. This new 
height of 17 feet results in a B of 10 feet for trucks 
and 15 feet for cars. Using the Barrier Nomograph a sub- 
tended angle of 165° is necessary to give a truck attenua- 
tion of 10 dB (see Figure 5-5) ; this results in a car 
attenuation of 11 dB. According to Figure 4-17 the total 
attenuation is then 10.5 dB, which meets the Design Goal. 

Several walls of varying heights and lengths can be 
constructed to provide the 10 dB truck attenuation. 
Working backwards through the nomograph, the heights 
and lengths of four possible walls are determined, as 
listed on Figure 5-6. Note from this figure that the 
lowest wall is extremely long. By increasing the wall 
height 3 feet (from 14 to 17 feet) , the necessary length is 
reduced a factor of three. However, to reduce wall length 
even further requires a much greater increase in wall height. 
Another important factor is consideration of other receivers; 
since the community extends 600 feet on either side of Re- 
ceiver 3, it would not be desirable to consider walls much 
shorter than the 2400 foot wall (1200 feet on each side of 



5-7 




♦ 



♦ 



* 



5-8 



FIGURE 5-6 
POSSIBLE BARRIER DIMENSIONS 



Subtended 
Angle Length, ft. Height, ft. Length x Height, sq. ft, 



175° 


7200 


14 


100,800 


170° 


3600 


16 


57,600 


165° 


2400 


17 


40,800 


160° 


1800 


24 


43,200 



5-9 



the receiver, from Station 88 to Station 112). Thus, based on 
all considerations the 17 foot high, 2400 foot long wall at 
this location seems to be the best choice at this point in 
the analysis. 

Using the Barrier Nomograph, the attenuation at Receiver 4 is 
seen to be 7.5 dB for this wall, which exceeds the required 
6 dB. 

Since the roadway curves, the barrier will wrap around Receivers 
3 and 4, and thus the wall need not extend a full 1200 feet to 
the left to provide the required attenuation for these receivers. 
However, the attenuation requirements for Receivers 1 and 2 
cannot be satisfied unless the wall is indeed extended further 
to the left. Using the Barrier Nomograph it can readily be 
determined that the 17 foot barrier should begin approximately 
at Station 83. 

For Receivers 5 and 6, the wall extends just far enough (to 
Station 112) to provide the Design Goal attenuations. If 
additional receivers were located to their right, the wall 
would have to be extended as necessary, or projected away 
from the highway towards the community, to provide the 
required subtended angle. 

To summarize, a wall of 17 foot height, located 3 feet from 
the shoulder (15 feet from the edge of the near lane) , and 
extending for 2900 feet along the roadway (1700 feet to the 
left of Receiver 3 and 1200 feet to the right from Stations 
83 to 112, provides the Design Goal attenuation for all 
critical receivers. In a similar manner, walls of different 
heights and lengths can be designed for other locations; since 
a wide right-of-way is available, locations in the middle of 
the right-of-way and near the right-of-way line could be 
evaluated. 

5-10 



I 



Based on discussions with community groups, the barrier 
materials under consideration should include both masonry 
blocks and wood. For comparison purposes a basic concrete 
wall is also under consideration. Climatic conditions 
dictate the need for weathering treatments in the barrier 
design. Also, the proximity of the barrier to the highway 
indicates the need for a safety barrier. 

Figure 5-7 shows a Design Option Worksheet incorporating 
these various considerations for the 17-foot barrier 
described above. The Cost Factor Worksheet for these 
options is presented in Figure 5-8; total costs are based 
on a city index of 95, and 1975 and current cost indices 
of 111 and 120, respectively. Finally, Figure 5-9 is a 
sample Design Evaluation Worksheet. From the information 
displayed on this worksheet (when all locations and options 
are included) , a single design can be selected which best 
satisfies acoustic and functional requirements and cost 
constraints. 

5-2. Parallel Barrier Example 

For the same highway/community configration examined in 
Section 5-1, assume that another 17-foot barrier is to be 
built on the opposite side of the roadway to protect a 
community in that area. This barrier will also be located 
3 feet from the shoulder (15 feet from the near lane) , but 
will begin at Station 96 and proceed to the right for 2000 
feet. 



5-11 



DESIGN OPTION WORKSHEET 



LOCATION NUK3ER 





Pos i t i on / 


Height / Length 




MATERIAL 


No. 1 


"No. 2 


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FIGURE 5-7 Design Option Worksheet for Basic Example 

5-12 



♦ 



COST FACTOR WORKSHEET 

















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FIGURE 5-8 Cost Factor Worksheet for Basic Example 

5-13 



DESIGN EVALUATION WORKSHEET 







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FIGURE 5-9 Design Evaluation Worksheet for Basic Example 

5-14 



♦ 



The impact of this second barrier on the design of the first 
barrier is determined using the Parallel Barrier Nomograph. 
The barrier separation W is 14 6 feet, the receiver to barrier 
distance D B for the closest receiver (No. 3) is 157 feet, and 
the barrier height H is 17 feet. The receiver is clearly in 
Region I with a height H R of 5 feet. From the preceding ex- 
ample, the barrier attenuation at this receiver for truck 
sources is 10 dB. Using the Barrier Nomograph the attenuation 
for truck sources for a receiver at ground level (H R = 0) is 
found to be 10.5 dB. 

Figure 5-10 illustrates the use of the Parallel Barrier Nomo- 
graph with these values (solid line) to determine that the 
degradation in barrier performance due to the second barrier 
is 4.5 dB. The resulting barrier noise reduction is there- 
by reduced to 5.5 dB, well below design requirements. 

The dashed line on Figure 5-10 show that use of an absorptive 
treatment on the barrier with a noise reduction coefficient 
of 0.6 will reduce ABAR to 1 dB; an absorptive treatment with 
NRC =0.8 will reduce ABAR to within one-half dB, essentially 
eliminating the multiple reflection effects. 

Figures 5-11 and 5-12 show design options and costs, respec- 
tively, of various alternative barrier designs which incor- 
porate absorptive treatments. 

5-3. Example of Variation in Highway Configuration 

Refer again to Figure 5-1. For this example the highway is 
depressed by five feet up to Station 96, then transitions at 
2% to an at-grade facility from Station 98 + 50 on. The 



5-15 




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5-16 



DESIGN OPTION WORKSHEET 



LOCATION NUMBER 





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FIGURE 5-11 Design Option Worksheet for Absorptive Barrier Designs 

5-17 



COST FACTOR WORKSHEET 



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GURE 5-12 Cost Factor Worksheet for Absorptive Barrier Designs. 

5-18 



sides of the cut have a 2:1 slope, so that the top of the cut 
is 10 feet from the edge of the shoulder. 

In order to provide the required attenuation for Receivers 1 
and 2 as indicated in Figure 5-2, a barrier placed along the 
top of the cut slope which transitions into the 17 foot barrier 
located 3 feet from the shoulder can be used. For the same 
length barrier as in the at-grade example (i.e., beginning 
at Station 83) , the height of the barrier along the depressed 
section need only be 13 feet. Figure 5-13 shows profiles of 
the roadway and barriers, for both the original at-grade 
facility and the current example with a depressed section. 
Note that the 17 foot barrier should begin no later than 
Station 96, to avoid creating a poorly shielded section as 
the traffic emerges from the depression. 

Figure 5-14 illustrates different approaches which can be 
taken to connect the walls. Note that if the walls are not 
connected, there should be an overlap provided, and absorp- 
tive treatment applied along the overlap section. 

Estimated costs for this segmented wall are easily determined 
by defining the cost factors and then total costs for each 
section, and then adding. 

One final word of caution is in order: once a barrier design 
option has been selected, any design such as this which is 
complicated by variations in highway configuration, terrain 
irregularities, the presence of ramps, etc, should be evaluated 
by computer to ensure that weak spots have not been overlooked. 



5-19 



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APPENDIX A 
REFERENCE DRAWINGS FOR WALLS AND BERMS 



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I 



APPENDIX B 
REFERENCE DRAWINGS FOR BARRIERS ON ELEVATED STRUCTURES 



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APPENDIX C 
REFERENCE DRAWINGS FOR ABSORPTION TREATMENTS 



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APPENDIX D 
DESIGN EXAMPLES FOR EXISTING NOISE BARRIERS 



D-l 



APPENDIX D 
DESIGN EXAMPLES FOR EXISTING NOISE BARRIERS 



The examples presented herein are intended to illustrate the 
type of results attainable through use of the barrier design 
procedure contained in Chapter 4. The highway sites chosen 
for the examples are sites at which actual noise barriers 
have been constructed by various state highway departments. 
In all cases, field-measured barrier attenuation data have 
been selected as noise reduction requirements for use in the 
design procedure. Design options are developed based on 
construction drawings and reports relating to the existing 
barrier sites. Finally, costs for each option are defined, 
referenced back to the date of actual barrier construction. 
Thus, the results of each example consist of a set of possible 
design options which are expected to provide the same noise 
reduction as the existing barrier, as well as comparative 
construction costs for these options. 



• 



• 



• 



D-2 



EXAMPLE 1; MINNEAPOLIS, MINNESOTA CPROSPECT PARI^) 
1-94 CHESTBOUNDl 

The existing noise barrier at this site consists of a pre- 
cast concrete panel wall, 35^8 ft. long and 10-23 ft. high. 
It was constructed in the summer of 197^ at a cost of $4.53 
per sq. ft. 

For the purposes of this example, an 800 ft. highway element 
is considered, from station 185 to 193. The object is to 
obtain alternative designs for this section, assuming it to 
be part of a continuous barrier. Thus, a subtended angle 
(6) of 180 ° is assumed in the calculations. Due to the 
limited distance between the edge of the traveled way and 
Frontage Rd . , only one barrier location option is considered. 
A design attenuation goal of 12 dBA is assumed for an observer 
location at a nearby residence. On this basis, a height of 
lh ft. is calculated, using the barrier nomograph procedure. 
A profile drawing of the barrier site, indicating source, 
observer and barrier locations, is given in Figure 1-1. 

Selected design options for the chosen barrier location are 
presented in Table 1-1. The table lists the barrier design 
codes and descriptions as well as the various constraints and 
additional treatment options. Note that construction of an 
earth berm has been ruled out, due to the limited right-of- 
way available. 

The definition of cost factors for the various barrier design 
options is illustrated in Table 1-2. Total estimated costs 
for each option are also presented, referenced to the date 
and location of construction. A city index of 97 and an 
inflation index (to 1975) of 111.2 are assumed in the calculations 



D-3 



ThLe approximate actual cost of tlie 80Q ft. section was $76,000, 

based on a height of 21 ft, for this section at $4.53 per sq. 

ft. Note that the predicted costs for concrete, masonry and m 

wood barrier designs range between $56,000 and $78,000. 

Predicted costs for steel barrier designs are significantly 

higher, in excess of $100,000. 



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D-5 



DESIGN OPTION WORKSHEET 



LOCATION NUMBER 





Position / 


Height / Length 






MATER 1 AL 


No. 1 


No. 2 




No. 3 


21/ 14 / 800 


/ / 


/ / 


Pre-Cast 
Concrete 


C-8-S 






C-8,2-S 






C-8.6-S 






Concrete 

Masonry 
Block 


M-6-S 






M-6.4-S 






M-6.5-S 






Steel 


S-5-S 






S-5.1-S 






S-5.3-S 






Wood 


w-3-s 






W-5.5-S 






W-4.4-S 






Wi nd Load i ng 
Aesthet ics 
Weather i ng 


k0 lb/ft 2 

YES 

YES 


Safety Barrier YES 




Absorption NO 




Other Comments 








DES 1 GN CODE 


DESCR 1 PT 1 ON 


NOISE REDUCTION 
LIMITED ? 


C-8 


Concrete w/integral color 


NO 


C-8,2 


Concrete w/integral color + sandblast 


NO 


C-8, 6 


Concrete w/integral color + rubber mat inserts 


NO 


M-6 


Masonry w/fntegral color 


NO 


M-6,*f 


Masonry w/integral color + combed units 


NO 


M-6, 5 


Masonry w/integral color + split face 


NO 


S-5 


Steel w/weathering 


NO 


S-5,1 


Steel w/weathering + sheet metal trim 


NO 


S-5.3 


Steel w/weathering + sheet metal trim £ stuccc 


NO 


w-3 


Wood w/preservat ive 


NO 



♦ 



• 



TABLE 1-1. EXAMPLE 1 - BARRIER DESIGN OPTIONS 
D-6- 



♦ 



DESIGN OPTION WORKSHEET 



LOCATION NUMBER 





Position / 


Height / Length 






MATERIAL 


No. 1 


No. 2 




No. 3 


21/14 / 800 


/ / 


/ / 


















































































Wind Loading 


Safety Barrier 


Aesthet ics 


Absorpt ion 


Weather i ng 


Other Comments 




DES 1 GN CODE 


DESCRI PT ION 


NOISE REDUCTION 
LIMITED ? 


W-5,5 


Wood w/stain (both sides) 


NO 


w-M 


Wood w/painting (both sides) 


NO 



















































TABLE 1-1. EXAMPLE 1 - BARRIER DESIGN OPTIONS (cont'd) 

D-7 



COST FACTOR WORKSHEET 

















Wine 


Loadir 


'9 40 lbs. per 


Des ign 

Code 


Loc. 

No. 


Ht. 
Ft. 


Length 
Ft. 


COST FACTORS 


TOTAL COST 


Bas ic 


Weather/ 
Aesthet. 
Treatmts 


Safety 
Barrier 


Absorpt ive 
Treatments 


TOTAL 


C-8-S 




14 


800 


79.10 


0.33 


12.08 


-- 


91.51 


63,700 


C-8.2-S 




14 


. 800 


79-10 


3.23 


12.08 


-- 


94.41 


65,700 


C-8.6-S 




14 


800 


79.10 


12.24 


12.08 


— 


103.42 


72,000 


M-6-S 




14 


800 


61.78 


6.60 


12.08 


__ 


80.46 


56,000 


M-6.4-S 




14 


800 


61.78 


13.84 


12.08 


-- 


87.70 


61,000 


M-6.5-S 




14 


800 


61.78 


38.80 


12.08 


-- 


112.66 


78,400 


S-5-S 




14 


800 


132.99 


3.55 


12.08 


.- 


148.62 


103,400 


S-5J-S 




14 


800 


132.99 


9.99 


12.08 





155.06 


107,900 


S-5.3-S 




14 


800 


132.99 


26.09 


12.08 


__ 


171.16 


119,100 


W-3-S 




14 


800 


66.91 


3.92 


12.08 


-- 


82.91 


57,700 


W-5,5-S 




14 


800 


66.91 


4.85 


12.08 


-- 


83.84 


58,400 


W-4,4-S 




14 


800 


66.91 


6.44 


12,08 


— 


85.43 


59,500 
















































































































































































































































4 










































































- 









sq. ft 



TABLE 1-2. 



EXAMPLE 1 - COST FACTOR DETERMINATION 
D-8 



EXAMPLE 2: MINNEAPOLIS, MINNESOTA (MINNEHAHA CREEK) 
I-35W 

The existing noise barrier at this site consists of parallel, 
non-absorptive wooden walls on landscaped earth mounds. The 
walls are pressure treated and are faced with vertical battens 
The barrier was constructed in the fall of 1972 at a cost of 
$100 per ft. 

For the purposes of this example, only the northbound side 
of the highway is considered, except that the reflection 
effects from a parallel barrier are taken into account. A 
design attenuation goal of 6 dBA is assumed for an observer 
location on a residential street (E. 53rd St.). In addition, 
a barrier length of 1900 ft. (station 97-116) is assumed 
to be required to protect other observer locations along 
the highway. Using the barrier design procedure, three 
geometrical options are identified as follows: 

1. Pr = 16 ft. 2. Pr = 56 ft. 3. Pr = 96 ft. 
H = 8 ft. H = 12 ft. h = 17 ft. 

L = 1900 ft. L = 1900 ft. L = 1900 ft. 

where: P R = position of barrier (distance to roadway) 
H = barrier height 
L = barrier length 

A profile drawing of the barrier site, indicating the source, 
observer and barrier locations, is given in Figure 2-1. 



D-9 



Since a parallel barrier is to be constructed, the need for 
applying acoustically absorptive material on the highway 
side of the barrier needs to be considered. The nomograph 
method of the barrier design procedure estimates a degradation 
(ABAR) of 4 dBA for 8 ft. sources (trucks) and 6 dBA for zero 
ft. sources (autos), assuming the closest -in barrier location. 
Application of absorptive linings is expected to reduce the 
degradations to 1 dBA and 3 dBA, respectively. Thus, the total 
degradation is reduced from approximately 5 dBA to 2 dBA. 
Therefore, absorptive linings are considered in the barrier 
design. 

Selected design options for the chosen barrier locations are 
presented in Table 2-1. The table lists the barrier design 
codes and descriptions as well as the various constraints 
and additional treatment options. Note that a combination 
earth berm and wooden wall is considered for location 2 only, 
due to space restrictions. Note also that a safety barrier 
is required for location 1 only, since this location is less 
than 30 feet from the highway. 

The definition of cost factors for the various barrier 
design options is illustrated in Table 2-2. Total estimated 
costs for each option are also presented, referenced to the 
date and location of construction. A city, index of 97 and 
an inflation index (to 1975) of 130.0 are assumed in the 
calculations . 



D-10 



t 



The approximate actual cost of the i860 ft. wall was $188,000 
The predicted costs are seen to rise sharply with increasing 
barrier distance from the highway. Choosing a close-in 
position takes advantage of the pre-barrier ground profile. 
Finally, note that the concrete and steel designs are 
significantly more expensive than the other material options. 



» 



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D-12 



♦ 



DESIGN OPTION WORKSHEET 



LOCATION NUMBER 





Position / 


Height / Length 




MATERIAL 


No. 1 


No. 2 


No. 3 


16 / 8 / 1500 


b6 / 12 / iyuu 


96 / 17 / 1900 


Pre-Cast 
Concrete 


C-8-S-a5(2) 


C-8-a5(2) 


C-8-a5(2) 


C-8,5-S-a5(2) 


C-8,5-a5(2) 


C-8,5-a5(2) 








Concrete 

Masonry 
Block 


M-S-al 


M-al 


M-al 


M-S-al(l) 


M-al (1) 


M-al (1) 








Steel 


S-5-S-a6 


S-5-a6 


S-5-a6 


S-5-a7 


S-5-a7 


S-5-a7 








Wood 


W-3-S-a^ 


W-3-a4 


W-3-ait 


W-l r 2-S-a** 


W-3.2-a*f 


W-3,2-aA 








Wind Loading 


kO lb/ft 2 


Safety Barrier Position 1 only 


Aesthet ics 


YES 


Absorption YES 


Weather ing 


YES 


Other Comments 




DESIGN CODE 


DESCRI PT ION 


NOISE REDUCTION 
LIMITED ? 


C-8-a5(2) 


Concrete w/integral color + glass fiber/ 






weathering metal siding abs. treatment 


YES (by 2 dB) 


C-8,5-a5(2) 


Concrete w/integral color + reinforcing bar 






inserts + glass fiber/weathering metal siding 


yrc (l v o HB) 




abs treatment 




M-al 


Masonry w/resona^t cavity blocks 


YES (by 2 dB) 


M-al(l) 


Masonry w/resonant cavity blocks + painting 


YES (by 2 dB) 


S-5-a6 


Steel w/weathering sttel + glass fiber/wood 






abs. treatment 


YES (by 2 dB) 









TABLE 2-1. EXAMPLE 2 - BARRIER DESIGN OPTIONS 

D-13 



DESIGN OPTION WORKSHEET 



LOCATION NUMBER 





Position / 


Height / Length 






MATERIAL 


No. 1 


No. 2 




No. 3 


16/8 / 1900 


56 / 12 / 1900 


96/17 / 1900 


Earth Berm & Wooden 
Wall 




B(3)-l 4 ,W-3,2-ai* 












































































Wind Loading 


Safety Barrier 


Aesthet ics 


Absorpt ion 


Weather i ng 


Other Comments 






DES 1 GN CODE 


DESCR 1 PT 1 ON 


NOISE REDUCTION 
LIMITED ? 


S-5-a7 


Steel w/weathering steel + glass fiber/metal 






abs. treatment 


YES (by 2 dB) 


W-3-S-a4 


Wood w/preservat ive + glass fiber/wood facing 






abs. treatment 


YES (by 2 dB) 


W-3,2-S-al* 


Wood w/preservat ive + vertical battens + glass 






fiber/wood facing abs. treatment 


YES (by 2 dB) 


B(3)"l 


Berm w/3 : 1 slope + landscaping (combine with 


YES (by 2 dB) 




above wall, each 6 feet high) 

















TABLE 2-1. EXAMPLE 2 - BARRIER DESIGN OPTIONS (cont ' d" 

D-14 



COST FACTOR WORKSHEET 



Wind Loading kO lbs. per sq . ft 



1 




Loc. 

No. 


Ht. 

Ft. 


Length 
Ft. 


COST FACTORS 


TOTAL COST 


f 


Design 
Code 


Bas ic 


Weather/ 
Aesthet . 

Treatmts 


Safety 
Barrier 


Absorptive 
Treatments 


TOTAL 




C-8-S- 






















a5(2) 


1 


8 


1900 


41.59 


0.19 


12.08 


26.65 


80.51 


114,700 




C-8-a5(2) 


2 


12 


1900 


65,49 


0.28 


-- 


41.35 


107.12 


152,600 




C-8-a5(2) 


3 


17 


1900 


98.47 


0.39 


-- 


52.41 


151.27 


215,600 




C-8,5- 






















a5(2) 


1 


8 


1900 


41.59 


5.90 


12.08 


26,65 


86.22 


122,900 




C-8,5- 






















a5(2) 


2 


12 


1900 


65.49 


8.84 


-- 


41.35 


115.68 


164,800 




C-8,5- 






















a5(2) 


3 


17 


1900 


98.47 


12.51 


__ 


52.41 


163.39 


232,800 




M-S-al 


1 


8 


1900 


30.47 


-- 


12.08 


8.93 


51.48 


73,400 




M-al 


2 


12 


1900 


50.09 


— 


_- 


13.39 


63.48 


90,500 


1 


.M-al(l) 


3 


17 


1900 


71.30 


__ 





18.96 


90.26 


128,600 


1 


M-S-al (1) 


1 


8 


1900 


30.47 


2.03 


12.08 


8.93 


53.51 


76,300 




M-al (1) 


2 


12 


1900 


50.09 


3.04 


— 


13.39 


66.52 


94,800 




M-al(l) 


3 


17 


1900 


71.30 


4.30 


__ 


18.96 


94.56 


134,700 




S-5-S-a6 


1 


8 


1900 


60.72 


2.03 


12.08 


8.46 


83.29 


118,700 




S-5-a6 


2 


12 


1900 


105.71 


3.04 


-- 


12.70 


121.45 


173,100 




S-5-a6 


3 


17 


1900 


189.18 


4.30 


-- 


17.99 


211.47 


301,300 




S-S-a7 


1 


8 


1900 


60.72 


2.03 


12.08 


10.19 


85.02 


121,200 




S-5-a7 


2 


12 


1900 


105.71 


3.04 


_ _ 


15-32 


124.07 


176,800 




S-5-a7 


3 


17 


1900 


189.18 


4.30 


_ _ 


21.70 


215.18 


306,600 




W-3-S-a4 


1 


8 


1900 


30.39 


2.17 


12.08 


11.15 


55-79 


79,500 




W-3-a4 


2 


12 


1900 


53.06 


3.33 


— 


17-40 


73.79 


105,200 




V.'-3-a4 


3 


17 


1900 


94.81 


5.21 


-- 


24.66 


124.68 


177,700 




W-3,2-S- 






















a4 


1 


8 


1900 


30.39 


3.20 


12.08 


11.15 


56.82 


81,000 


a 


W-3.2-a4 


2 


12 


1900 


53.06 


5.14 


-- 


17.40 


75.60 


107,700 



TABLE 2-2. EXAMPLE 2 - COST FACTOR DETERMINATION 

D-15 



COST FACTOR WORKSHEET 

















Wine 


1 Loadir 


'9 


Des ign 
Code 


Loc. 

No. 


Ht. 
Ft. 


Length 
Ft. 


COST FACTORS 


TOTAL COST 


Bas ic 


Weather/ 
Aesthet . 

Treatmts 


Safety 
Ba r r ier 


Absorptive 
Treatments 


TOTAL 


W-3,2-a4 


3 


17 


1900 


94.81 


8.14 


_- 


24.66 


127.61 


181,800 


(B(3)-l J 


( 2 ) 


I 6 ) 


1900 














lw-3.2-a4| 


1.1 


LI 


1900 


28.60 


29.63 


_ _ 


7.82 


66.05 


94.100 























































































































































































































































































































































































































































































































• 



• 



« 



TABLE 2-2. EXAMPLE 2 - COST FACTOR DETERMINATION (cont'd) 

D-16 



EXAMPLE 3: WEST HARTFORD, CONNECTICUT 
1-84 (EASTBOUND) 

The existing noise barrier at this site consists of a land- 
scaped earth berm, 1800 ft. long and approximately 14 ft. 
high. It was constructed in June, 1974 at a total cost of 
$150,000. 

For the purposes of this example, two observer locations are 
considered as follows: 

A. At curb, near 45 Wilfred St., along highway station 363 

B. At curb, near 123 Wilfred St., along highway station 353 

The design attenuation goals are 10 dBA for location A and 
4 dBA for location B. Using the barrier design procedure, 
based on the more critical observer location A, three 
geometrical options are identified as follows: 

1. P R = 15 ft.(A&B) 2. P R = 60 ft. (A) 3. P R = 100 ft. (A) 

= 40 ft. (B) = 65 ft. (B) 

H= 23 ft. H = 14 ft. H = 11.5 ft. 

L= 1400 ft. L = 1400 ft. L = 1400 ft. 

where: P R = position of barrier (distance to roadway) 
H = barrier height 
L = barrier length 

Note that the barrier positions vary with respect to the 
highway, due to variations in the right-of-way width along the 
length of the barrier. Profile drawings of the barrier site, 



D-17 



indicating source, observer and barrier locations, are given 
in Figure 3-1 « Figure 3-2 presents plan views of the barrier 
options. Although the options are initially developed based 
on the attenuation goal at observer location A, repeated 
checks of the resultant predicted attenuations for location B 
ensure that the selected options also satisfy the goal at the 
latter observer location. 

Selected design options for the chosen barrier locations are 
presented in Table 3-1 • The table lists the barrier design 
codes and descriptions as well as the various constraints 
and additional treatment options. Note that an earth berm is 
considered for location 2 only, due to space requirements. In 
addition, safety barriers are required for all options at 

location 1, due to the close proximity to the highway. 



The definition of cost factors for the various barrier design 
options is illustrated in Table 3-2. Total estimated costs for 
each option are also presented, referenced to the date and 
location of construction. A city index of 97 and an inflation 
index (to 1975) of 112.0 are assumed in the calculations. 

The predicted barrier costs are seen to drop sharply with 
increasing barrier distance from the highway due to the 
pre-barrier ground profile. The barrier materials, listed 
in order of increasing costs, are masonry, wood, concrete, 
'earth berm and steel. 



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» 



DESIGN OPTION WORKSHEET 



LOCATION NUMBER 



» 





Position / 


Height / Length 






MATERIAL 


No. 1 


No. 2 




No. 3 


15/23 / 1400 


40-60 / 14 / 1400 


65-100/11.5 / lt00 


Pre-Cast 
Concrete 


C-8.S 


C-8 


C-8 


C-8, 1-S 


C-8, 1 


C-8, 1 








Concrete 

Masonry 

Block 


M-6-S 


M-6 


M-6 


M-6, 1-S 


M-6,1 


M-6,1 








Steel 


S-5-S 


S-5 


S-5 


S-5,2-S 


S-5, 2 


S-5, 2 








Wood 


W-3-S 


W-3 


W-3 


W-3, 1-S 


W-3,1 


W-3,1 








Wind Loadinq 30 lb/ft 2 


Safety Barrier Position 1 only 


Aesthetics YES 


Absorption N0 


Weatherinq YES 


Other Comments 






DESIGN CODE 


DESCRIPT ION 


NOISE REDUCTION 
LIMITED ? 


C-8 


Concrete w/integral color 


NO 


C-8.1 


Concrete w/integral color + exposed aggregate 


NO 


M-6 


Masonry w/integral color 


NO 


M-6,1 


Masonry w/integral color + vertical scored bloc 


k NO 


S-5 


Steel w/weathering steel 


NO 


S-5,2-5 


Steel w/weathering steel + sheet metal trim & 






wood veneer 


NO 


W-3 


Wood w/preservative 


No 


W-3,1 


Wood w/preservative + plywood facing 


NO 


B(2)-l 


Earth berm w/2:l slope + landscaping 


NO 



TABLE 3-1. EXAMPLE 3 - BARRIER DESIGN OPTIONS 
D-21 



» 



DESIGN OPTION WORKSHEET 



LOCATION NUMBER 





Position / 


Height / Length 






MATERIAL 


No. 1 


No. 2 




No. 3 


15/23 / .1400 


40-60 / 14 / 1400 


65-100/ 11.5/ 1 400 


Earth Berm 




B(2)-l 












































































Wind Loading 


Safety Barrier 


Aesthet ics 


Absorpt ion 


Weather i ng 


Other Comments 




DE5 1 GN CODE 


DESCR 1 PT 1 ON 


NOISE REDUCTION 
LIMITED ? 































































♦ 



♦ 



TABLE 3-1. EXAMPLE 3 - BARRIER DESIGN OPTIONS (cont'd) 

D-22 



• 



COST FACTOR WORKSHEET 

















Wine 


1 Loadir 


ig 30 lbs. per 


Des ign 
Code 


Loc. 
No. 


Ht. 
Ft. 


Length 
Ft. 


COST FACTORS 


TOTAL COST 


Bas ic 


Weather/ 
Aesthet . 
Treatmts 


Safety 

Barrier 


Absorptive 
Treatments 


TOTAL 


C-8-S 


1 


23 


1400 


132.21 


0.53 


12.08 


-- 


144.82 


176,400 


C-8 


2 


111 


1400 


80.71 


0.33 


-- 


— 


81.04 


98,700 


C-8 


3 


11.5 


1400 


62.11 


0.27 


-- 


— 


62.38 


76,000 


C-8.1-S 


1 


23 


1400 


132.21 


6.61 


12.08 


— 


150.90 


183,800 


C-8,1 


2 


14 


1400 


80.71 


4.04 


-- 


-- 


84.75 


103,200 


C-8, 1 


3 


11.5 


1400 


62.11 


3.32 


-- 


— 


65,43 


79,700 


M-6-S 


1 


23 


1400 


77.49 


10.85 


12.08 


— 


100.42 


122,312 


M-6 


2 


14 


1400 


55-40 


6.60 


-- 


-- 


62.00 


75,500 


M-6 


3 


11.5 


1400 


42.98 


5.43 


— 


-- 


48.41 


59,000 


M-6.1-S 


1 


23 


1400 


77.49 


22.75 


12.08 


— 


112.32 


136,800 


M-6, 1 


2 


14 


1400 


55.40 


13.84 


— 


-- 


69.24 


84,300 


M-6,1 


3 


11.5 


1400 


42.98 


11.38 


— 


-- 


54.36 


66,200 


S-5-S 


1 


23 


1400 


279-33 


5.82 


12.08 


— 


297.23 


362,000 


S-5 


2 


1*4 


1400 


118.96 


3.55 


__ 


-- 


122.51 


149,200 


S-5 


3 


11.5 


1400 


92.91 


2.91 


— 


— 


95.82 


116,700 


S-5.2-S 


1 


23 


1400 


279-33 


30.68 


12.08 


-- 


322.0S 


392,300 


S-5, 2 


2 


14 


1400 


118.96 


18.69 


-- 




137.65 


167,700 


S-5, 2 


3 


11.5 


1400 


92.91 


15.34 


-- 


-- 


108.25 


131,800 


W-3-S 


1 


23 


1400 


139-6/ 


7.46 


12.08 




159.21 


193,900 


W-3 


2 


14 


1400 


59.48 


3.59 


-- 


— 


63.07 


76,800 


W-3 


3 


11.5 


1400 


46. 4< 


2.97 


-- 


-- 


49.4; 


60,200 


W-3.1-S 


1 


23 


1400 


139-67 


20.95 


12.08 


-- 


172.7C 


210,300 


W-3,1 


2 


14 


1400 


59.48 


11.80 


-- 


— 


71.28 


86,800 


W-3,1 


3 


11.5 


1400 


46.46 


9.72 


-- 


— 


56.18 


68,400 


B(2)-l 


2 


14 


1400 


21.7^ 


41.63 


-- ' 


-- 


63 - 35 


73,200 































































sq. ft 



TABLE 3-2. EXAMPLE 3 - COST FACTOR DETERMINATION 

D-23 



EXAMPLE 4: SAN GABRIEL, CALIFORNIA 
1-10 (WESTBOUND) 

The existing noise barrier at this site consists of a concrete 
block wall, 1925 ft. long and 13 ft. high. The wall has an 
architectural facing of brick and stucco, with a top of red 
tiles, and is curved at both ends. It was constructed in 
December, 1973 at a total cost of $145,000. 

For the purposes of this example it is assumed that barrier 
construction is limited to the highway element between 
stations 457 and 475. A design attenuation goal of 14 dBA 
is assumed for an observer location 100 ft. from the near 
edge of the westbound lane, at highway station 471. Utilizing 
the barrier design procedure, it is determined that for a 
maximum length, straight barrier (1800 ft. long) a barrier 
height of 33 ft. is required. Since this height is deemed 
impractical, consider curving back the two ends of the 
barrier in order to provide an increased effective length 
by increasing the subtended angle (6). This approach results 
in an allowable barrier height of 16 ft. with an overall 
length of 2000 linear ft. as shown in the profile drawing of 
Figure 4-1 and the plan view of Figure 4-2. Note that due 
to limited distance between the right-of-way limit and an 
on-ramp traffic lane, only one barrier location is considered 
in this example. 

Selected design options for the chosen barrier location are 
presented in Table 4-1. The table lists the barrier design 
codes and descriptions as well as the various constraints and 
additional treatment options. Note that construction of an 



D-24 



earth berm is not practical in this case due to the limited 
right-of-way and that a safety barrier is required due to 
the close proximity to the on-ramp traffic lane. 

The definition of cost factors for the various barrier 
design options is illustrated in Table 4-2. Total estimated 
costs for each option are also presented, referenced to the 
date and location of construction. A city index of 96 and 
an inflation index of 118.8 are assumed in the calculations. 

Note that the actual cost of the barrier is comparable to 
predicted costs for wood and masonry walls and is $25,000 
to $45*000 less than the predicted costs for concrete 
barriers. The predicted costs for the steel barrier options 
are significantly greater than costs for the other material 
types . 



D-25 



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D-27 



DESIGN OPTION WORKSHEET 



LOCATION NUMBER 





Position / 


Height / Length 






MATERIAL 


No. 1 


No. 2 




No. 3 


10 / 16 /2000 


/ / 


/ / 


Pre-Cast 
Concrete 


C-S 






C-9.9-S 






C-4-S 






Concrete 
Masonry 

Block 


M-S 






M-7.7-S 






M-3-S 






Steel 


S-5-S 






S-4.4-S 






S-5,3-S 






Wood 


W-3-S 






W-4.4-S 






W-3.2-S 






Wind Loadinq 30 lb/ft 2 


Safety Barrier YES 


Aesthetics YES 


Absorption NO 


Weatherinq YES 


Other Comments 






DESIGN CODE 


DESCR 1 PT ION 


NOISE REDUCTION 
LIMITED ? 


C 


Concrete untreated 


NO 


C-9,9 


Concrete w/painting (both sides) 


NO 


C-k 


Concrete w/wood form inserts 


NO 


M 


Masonry untreated 


NO 


M-7,7 


Masonry w/painting (both sides) 


NO 


M-3 


Masonry w/V slump block 


NO 


S-5 


Steel w/weathering 


NO 


S-k,k 


Steel w/painting (both sides) 


NO 


S-5, 3 


Steel w/weathering + sheet metal trim & stucco 


NO 









• 



♦ 



TABLE d-1. EXAMPLE k - BARRIER DESIGN OPTIONS 

D-28 



• 



I 



DESIGN OPTION WORKSHEET 



LOCATION NUMBER 



» 





Position / 


Height / Length 






MATERIAL 


No. 1 


No. 2 




No. 3 


10/16 / 2000 


/ / 


/ / 


















































































Wind Loading 


Safety Barrier 


Aesthet ics 


Absorpt ion 


Weathering 


Other Comments 




DES IGN CODE 


DESCRI PT ION 


NOISE REDUCTION 
LIMITED ? 


W-3 


Wood w/preservat ive 


NO 


W-4,4 


Wood w/painting (both sides) 




W-3,2 


Wood w/preservat ive + vertical battens 


NO 













































TABLE 4-1. EXAMPLE 4 - BARRIER DESIGN OPTIONS (cont'd) 

D-29 



» 



COST FACTOR WORKSHEET 

















Wine 


1 Loading 30 lbs . per 


Des ign 
Code 


Loc . 

No. 


Ht. 
Ft. 


Length 
Ft. 


COST FACTORS 


TOTAL COST 


Bas ic 


Weather/ 
Aesthet. 
Treatmts 


Safety 
Barrier 


Absorptive 
Treatments 


TOTAL 


c-s 




16 


2000 


93.66 


-- 


12.08 


-- 


105.74 


171,300 


C-9.9-S 




16 


2000 


93.66 


7.14 


12.08 


-- 


112.88 


182,900 


C-4-S 




16 


2000 


93-66 


11.96 


12.08 


-- 


117.70 


190,700 


M-S 




16 


2000 


62.51 


-- 


12.08 


— 


74.59 


120,800 


M-7.7-S 




16 


2000 


62.51 


8.10 


12.08 


— 


82.69 


134,000 


M-3-S 




16 


2000 


62.51 


36.80 


12.08 


— 


111.39 


180,500 


S-5-S 




16 


2000 


148.12 


4.05 


12.08 


-- 


164.25 


266,100 


S-4.4-S 




16 


2000 


148.12 


5.52 


12.08 


-- 


165.72 


268,500 


S-5.3-S 




16 


2000 


148.12 


29.81 


12.08 


-- 


190.01 


307,800 


W-3-S 




16 


2000 


74.06 


4.29 


12.08 


-- 


90.43 


146,500 


W-4.4-S 




16 


2000 


74.06 


7.35 


12.08 


-- 


93.50 


151,500 


W-3.2-S 




16 


2000 


74.06 


7.05 


12.08 


-- 


93.19 


151,000 










































































































































































































■ 











































































■ 
































..... 


- 









sq. ft, 



TABLE 4-2. EXAMPLE 4 - COST FACTOR DETERMINATION 

D-30 



EXAMPLE 5: ALLEN PARK, MICHIGAN 
1-75 (SOUTHBOUND) 

The existing noise barrier at this site consists of a wooden 
wall, 2700 ft. long and 13-5 ft. high. The wall was con- 
structed in the spring of 1974 at a total cost of $181,000. 

For the purposes of this example, consider a straight barrier, 
2750 ft. long, extending between highway stations 745 and 772 + 
50. Due to the limited right-of-way (30 ft. between edge of 
near lane and R/W limit), only one barrier position is con- 
sidered. A design attenuation goal of 11 dBA is assumed for 
an observer location 61 ft. from the edge of the near lane 
along highway station 761. For the above conditions, the 
barrier nomograph procedure indicates a required barrier height 
of 12.5 ft. A profile drawing of the barrier site, indicating 
the source, observer and barrier locations, is given in 
Figure 5-1. 

Selected design options for the chosen barrier locations are 
presented in Table 5-1. The table lists the barrier design 
codes and descriptions as well as the various constraints and 
additional treatment options. Note that an earth berm is not 
feasible in this case, due to space restrictions, and that a 
safety barrier is required, due to the close proximity to the 
highway. 

The definition of cost factors for the various barrier design 
options is illustrated in Table ,5-2. Total estimated costs 
for each option are also presented, referenced to the date and 
location of construction. A city index of 95 and an inflatior 
index of 114.4 are assumed in the calculations. 



D-31 



The predicted costs for the wood barrier options are seen to be 
less than the actual cost. Note also that costs for the steel 
barrier options are much higher than the costs for the other 
material types. 



♦ 



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D-33 



DESIGN OPTION WORKSHEET 



LOCATION NUMBER 





Position / 


Height / Length 










MATERIAL 


No. 1 


No. 2 






No. 3 


41 /l 2.5 /2750 


/ / 


/ 


/ 


Pre-Cast 


C-S 






C-2-S 






C-3-S 






Concrete 

Masonry 
Block 


M-S 






M-l-S 






M-2-S 






Steel 


S-5-S 






S-5.1-S 






S-5.2-S 






Wood 


w-3-s 






W-5.5-S 






W-5.5.1-S 






Wind Loading 
Aesthet ics 
Weathering 


30 lb/ft 2 Safety Barrier 
YES Absorption 
YES Other Comments 


YES 






NO 


















DESIGN CODE 


DESCRI PT ION 


NOISE REDUCTION 
LIMITED ? 


C 


Concrete untreated 


NO 


C-2 


Concrete w/sandblast 


NO 


C-3 


Concrete w/roughsawn random width board 


form 


NO 


M 


Masonry untreated 


NO 


M-l 


Masonry w/vertical scored block 


NO 


Mr 2 


Masonry w/6" slump block 


NO 


S-5 


Steel w/weathering 


NO 




S-5,1 


Steel w/weathering + sheet metal trim 


NO 


S-5, 2 


Steel w/weathering + sheet metal trim S 


wood ve 


leer NO 











♦ 



• 



TABLE 5-1. EXAMPLE 5 - BARRIER DESIGN OPTIONS 

D-34 



• 



DESIGN OPTION WORKSHEET 



LOCATION NUMBER 





Position / 


Height /Length 




MATERIAL 


No. 1 


No. 2 


No. 3 


11 / 12.5/ 2750 


/ / 


/ / 


















































































Wind Loading 


Safety Barrier 


Aesthet ics 


Absorpt ion 


Weather i ng 


Other Comments 




DESIGN CODE 


DESCRI PT ION 


NOISE REDUCTION 
LIMITED ? 


W-3 


Wood w/preservat ive 


NO 


W-5,5 


Wood w/stain (both sides) 


NO 


W-5,5,1 


Wood w/stain (both sides) + plywood facing 


NO 













































TABLE 5-1. EXAMPLE 5 - BARRIER DESIGN OPTIONS (cont'd) 

D-35 



COST FACTOR WORKSHEET 

















Wine 


Loading 30 lbs. per 


Des ign 
Code 


Loc. 

No. 


Ht. 
Ft. 


Length 
Ft. 


COST FACTORS 


TOTAL COST 


Bas ic 


Weather/ 
Aesthet . 
Treatmts 


Safety 
Barrier 


Absorptive 
Treatments 


TOTAL 


C-S 




12.5 


2750 


69.55 


-- 


12.08 


— 


81.63 


186,300 


C-2-S 




12.5 


2750 


69.55 


2.59 


12.08 


-- 


84.22 


192,200 


C-3-S 




12.5 


2750 


69.55 


8.34 


12.08 


— .. 


89.97 


205,400 


M-S 




12.5 


2750 


47.95 


__ 


12.08 


-- 


60.03 


137,000 


M-l-S 




12.4 


2750 


47.95 


6.47 


12.08 


-- 


66.50 


151,800 


M-2-S 




12.5 


2750 


47-95 


32.35 


12.08 


— 


92.38 


210,900 


S-5-S 




12.5 


2750 


103.33 


3.17 


12.08 


— 


118.58 


270,700 


S-5J-S 




12.5 


2750 


103.33 


.8.92 


12.08 


-- 


124.33 


283,800 


S-5.2-S 




12.5 


2750 


103.33 


16.69 


12.08 


-- 


132.10 


301,500 


W-3-S 




12.5 


2750 


.51.67 


3.22 


12.08 


— 


66.97 


152,900 


W-5.5-S 




12.5 


2750 


51.67 


4.36 


12.08 


-- 


68.11 


155,500 


W-5.5.1-S 




12.5 


2750 


51.67 


11.70 


12.08 


— 


75.45 


172,200 



































































































































































































































































































































sq. ft, 



TABLE 5-2. EXAMPLE 5 - COST FACTOR DETERMINATION 

D-36 



REFERENCES 



1-1 Simpson, M.A. , "Noise Barrier Attenuation: Theory 

and Field Experience," BBN Report No. 3200, February 
1976. 

1-2 Towers, D.A. , "Noise Barrier Catalogue," BBN Report 
No. 3201, February 1976. 

1-3 Pejaver, D. and Shadley, J., "A Study of Multiple 
Sound Reflections in Walled Highways and Tunnels," 
BBN Report No. 3202, February 1976. 

1-4 Hirtle, P.W., et al, "Catalogue of Sound Absorbing 
Treatments for Highway Structures," BBN Report No. 
3203, February 1976. 

2-1 Kurze, U.J. and Anderson, G.S., "Sound Attenuation 
by Barriers," Applied Acoustics 4, 35-53 (1971). 

2-2 Kugler, B.A. , Commins, D.E. and Galloway, W.J., 
"Design Guide for Highway Noise Prediction and 
Control," NCHRP 3-7/3, BBN Report No. 2739, 
Volume 1, November 197 4. 

2-3 Wesler, J.E., "Manual for Highway Noise Prediction," 
Transportation System Center Report DOT-TSC-FHWA- 
72-1, 1972. 

2-4 Gordon, C.G., et al, "Highway Noise - A Design Guide 
for Highway Engineers," NCHRP Report No. 117, 1971. 

2-5 Kugler, B.A. and Piersol, A.G., "Highway Noise - A 

Field Evaluation of Traffic Noise Reduction Measures," 
NCHRP Report No. 144, 1973. 

3-1 "Location, Selection and Maintenance of Highway 
Traffic Barriers," NCHRP Report No. 118, 1971. 

3-2 "Guide on Evaluation and Attenuation of Traffic Noise," 
AASHTO, 197 4. 

3-3 "Highway Design and Operational Practices Related 
to Highway Safety," AASHTO, 197 4. 

3-4 "Standard Specifications for Structural Supports 

for Highway Signs, Luminaries, and Traffic Signals," 
AASHTO, 1975. 



4-1 "A Policy on Design of Urban Highways and Arterial 
Streets/' AASHTO, 1973. 

4-2 "Fundamentals of Traffic Engineering," 8th Edition, m 
Institute of Transportation and Traffic Engineering, ^ 
UC Berkley. 

4-3 Tye, Edward J., "Median Barriers in California, 
Traffic Engineering, September 1975. 



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